In Sailor Moon, the destruction of the Kisenean Blossom leaves the senshi stranded on an asteroid on a collision course with the earth.
In the third season, Mugen is destroyed by the battle and the senshi are buried beneath the rubble. They're OK, though.
Bleach: After Chad and Uryu defeat Demora and Iceringer, the room they are in collapses, having been designed to do so if they were defeated.
Atem/Yami Yugi plays this role in the last episode of Yu-Gi-Oh!; after he is defeated in the Ceremonial Duel, the temple they're in begins to collapse.
In One Piece, Luffy's final kick against Arlong destroys Arlong Park, the building that they're in. In a filler arc, after Luffy defeats Don Atchino, his Atsu Atsu Fruit powers melt the Atchino family's iceberg base.
In the Arlong case, this is because Luffy's final attack was to kick Arlong through the building; it wasn't so much that the building was destroyed because the boss died as it was because the boss was smashed through all five floors of it.
In Code Geass: Nightmare of Nunnally, after Nunnally rejects opening Heaven's Door in favor of "tomorrow," resulting in her parents being erased from existence like they were in the original series, the cave in Kamine Island collapses.
Very popular in Saint Seiya. All of the OVA villains pull this one after being defeated, concluding with Seiya & Co. running for their lives.
Athena herself is one in the anime version of the Hades chapter: when she kills herself to attack Hades in his own domain, the Saints all but states that the main part of the Sanctuary is about to collapse now that Athena's cosmo doesn't sustain it anymore, and that is still standing only because it was the only one built by men (meaning that Athena's cosmo was simply protecting it from the ravages of time instead of enabling its very existence).
Played with in Dai-Guard, when the team find a dormant Heterodyne and wonder whether they should leave it be or destroy it before it wakes up. The eventually go with the former, which is good because while it was dormant it kept growing underground until its structure was holding up the entire Kyoto area and the only safe way to dispose of it was to wait until it eventually sank into the Earth's crust.
The ailing Princess in the Kokuboro arc of Kekkaishi created the castle and alternate dimension that shares the name of that storyline; the castle gradually decays and eventually collapses as her health deteriorates, to the point where the whole dimension completely collapses when she ultimately expires.
Hakumen no Mono from Ushio and Tora fits this trope perfectly. If Ushio's mom lets up the barrier and allows the yōkai of Japan to kill him, all the islands of Japan will sink with him
Tengen Toppa Gurren Lagann: When Simon defeats Lordgenome in Episode 15, all the Gunmen being piloted by his mooks deactivate. More to the point, so does the mountain-sized Humongous Mecha they were fighting on top of, causing it to rapidly collapse under its own weight. Pops up again when the Anti-Spiral are finally defeated. Not only does it destroy the enemy's galaxy-sized mecha, it also destroys their home planet and the very dimension they inhabited.
In Scryed, defeating Kyoji Mujo caused the warped base to fall apart. Justified since it was being sustained with Kyoji's Alter Power, with him dead, there was nothing supporting it.
In GaoGaiGar Final, when the heroes use the Goldeon Crusher to kill Pisa Sol, the whole UNIVERSE falls apart. Thankfully they were in an alternate universe, but still!
In Gankutsuou, the Count's headquarters begins collapsing seconds after he dies for no readily apparent reason.
Defeating King in Rave Master causes the tower the hero and his dad were fighting on to crumble. Their race to the bottom leads to a perfect Dropped a Bridge on Him moment. Except instead of a bridge what dropped was a...
Subverted in the Wizardry OVA, where although Werdna's death causes much trembling throughout the dungeon, the heroes are able to wait it out and then walk out.
Something similar happens in Vampire Hunter D: Bloodlust. Vampire castles apparently have No Ontological Inertia.
In the film version of Super Dimension Fortress Macross, Golg Bodolzer himself is wired into his ship's computer. When the hero shoots him down, the rest of the ship quickly follows. Though in a bit of a variation, what actually seems to happen is Bodolzer's death causes a malfunction in the ship's Fold System, causing random pieces of it to get teleported who-knows-where. Explosions happen as a result of this, and the ship is thoroughly wrecked, but its outer structure is still largely intact afterward.
In the first Tenchi Muyo! OVA, Tenchi bisectsKagato in their climactic battle. Somehow this causes Kagato's gargantuan spaceship that they were fighting inside of to also be sliced in half.
Invoked in Gold Digger: Julia defeats a warlord who enslaved his own people to fuel his power by tangling him up in chains around the pillars holding up his throne room, then knocking them out in a way to leave him as the "keystone" holding the whole thing together. If he tries to move to attack or free himself, tens of thousands of tons of stone come tumbling down on his head. The only way to get free would be to beg his subjects to free him. The rival Julia came to rescue notes that said warlord is likely to let himself starve to death first.
Jewel Of Darkness: After Midnight is defeated in her lair at the end of the Jump City Arc, Slade spirits her to safety, activating the base's self-destruct to cover their escape. Lampshaded by Beast Boy:
"And there's the post big fight self destruct."
Life In Manehattan: The Final Battle between the Manehattan Six and Nightmare Moon occurs in a Pocket Dimension facsimile of Manehattan created by the latter; when she's defeated, it starts to fall apart. Fortunately, Luna is able to carry them all to safety.
Through A Diamond Sky: Clu hangs a lampshade on this when killing The Baron causes his hideout to go to cascade failure. But Justified because of the base's shoddy construction and The Baron soaking up way too much power, destabilizing it further.
"Explain to me," Clu grumbled. "Why we take out the boss and this place decides to go into cascade failure?"
Films — Animation
At the end of The Pebbleandthe Penguin, Drake hurls a boulder at Hubie as a last-minute attempt to kill him, but he throws said boulder in the wrong direction, and as a result the boulder rolls back and crushes Drake to death before finally destroying enough pillars holding up his island causing it to crumble into the sea.
Yor: The Hunter from the Future, an old B-movie starring Reb Brown, has a cave inexplicably collapse after the strongest warrior of the tribe living there is defeated.
In the Spawn film, Jason Winn sets himself up as the ultimate load-bearing boss: He attaches a heart-rate sensor to himself, which will set off dozens of virus-bombs all over the world in the event of his death to deter assassinations (though how a would-be kill is supposed to know this ahead of time is anyone's guess). Spawn uses his nifty magic powers to just pull the sensor out of his body before turning him over to the cops.
The Lord of the Rings: Return of the King makes it even more extreme than the book: The death of Sauron causes the land around the entrance to the black gate to collapse into a pit, taking the orc army with it, while the area on which the good guys are standing forms a sort of rock outcropping.
Averted in the James Bond film The Man with the Golden Gun. Scaramanga's base/lair/thing begins to explode as soon as Bond kills Scaramanga, but this is due to the unrelated actions of a less-than-intelligent Bond Girl.
Justified in Inception: killing the dreamer makes their dream world spectacularly collapse.
Start with Book 7, Castle Death, and the destruction — in a volcanic eruption — of the title fortress of Kazan-Oud after the defeat of its evil Lord, Zahda. Though to be specific, it is the shattering of the Doomstone which induces this, since its magic was keeping the volcano at bay, and not just Zahda's death.
Averted in Book 12. If Helgedad is destroyed shortly after the defeat of Big Bad Gnaag, it's because Lone Wolf has brought a freaking magical bomb with him, causing a chain reaction that wipe out the whole evil capital city.
Played straight in Book 17, The Deathlord of Ixia, with the destruction of Big Bad Ixiataaga resulting in the collapse of the whole city of Xaagon as time is catching up with it.
Probably the earliest example (from 1470) of the Load-Bearing Boss, Sir Thomas Malory's Le Morte Darthur features a fight between Balin and King Pellam. Balin's sword breaks, so he steals an ornate spear that happens to be lying around.
And when Balin saw that spear, he gat it in his hand and turned him to King Pellam, and smote him passingly sore with that spear, that King Pellam fell down in a swoon, and therewith the castle roof and walls brake and fell to the earth, and Balin fell down so that he might not stir foot nor hand. And so the most part of the castle, that was fallen down through that dolorous stroke, lay upon Pellam and Balin three days.
Another early example is Edgar Allan Poe's classic Gothic tale The Fall of the House of Usher, first published in 1839, in which the eponymous house breaks in two and collapses when Roderick and Madeline die.
Their deaths don't actually cause the house to collapse. However, since the house was a metaphor for the family, it seems justified.
Dracula was apparently originally going to include a scene where Dracula's castle collapsed upon his defeat (though it would not have been a threat to anyone, since the climactic battle takes place outside of the castle).
Neal Stephenson's Snow Crash has a rare example of Load-Bearing Boss without a Collapsing Lair. Raven, a big mutant Aluet has a hydrogen bomb he carries around with on a motorcycle sidecar. It's hooked up to an implant that sends the detonation signal if his heart stops. (This, combined with his incredible fighting skills and use of undetectable glass knives, leads the main character to label him "The Baddest Motherf** ker in the world".)
Literary subversion: in Captain's Fury, fourth book of the Codex Alera series, one of the villains has managed to tie the ongoing calmness of a volcano in his homeland to his own survival via magic. Rather than waiting for the volcano to go boom upon the villain's eventual defeat, his rival Gaius Sextus actually uses this to defeat the villain in the first place by blowing the volcano up on top of the still-living villain, burying him and his entire capital city in volcanic ash a la Pompeii.
The villain had been inspired to do this by Lady Placida's more benevolent use of it in the previous book; she had used her powers to suppress destructive furies in her homeland that would be unleashed upon her death unless the proper steps were taken, forcing her husband into neutrality after the villain kidnapped her. She'd had no intention of using it as a weapon, and was merely trying to help her people.
In The Silver Chair by C.S. Lewis (one of the Chronicles of Narnia), the death of the Lady of the Green Kirtle causes not just her fortress, but her entire underground kingdom to be destroyed. The protagonists speculate that she had used sorcery to ensure this would happen as a means of posthumously avenging herself on her killer.
In another classic children's fantasy series, the Prydain Chronicles by Lloyd Alexander, we see this trope played out in the fiery collapse of the castle of Arawn, Lord of the Dead, in the land of Annuvin, when he is killed by the sword Dyrnwyn.
The destruction of the One Ring in The Lord of the Rings causes both the death of Sauron and his Dark Tower to collapse. It's explicitly noted earlier that the Ring's power was holding the thing up. It also causes the collapse of the Black Gate and the Teeth of Mordor (the guard towers by the gate).
In the Codex Alera, High Lord Kalare arranged things so that if he died, a volcano would erupt and destroy the city he was in. It backfired spectacularly when Gaius Sextus remotely triggered the volcano when no other enemies of Kalare were in the area.
 had this setup at one point. It was the reason Jaime killed Aerys: he found out about Aerys's plan to use wildfire to burn everything in King's Landing, including his family and all the innocent people, and decided that it could not be allowed to happen.
Justified in Sourcery, where Coin created the huge miles-high tower (which has become the new home for wizards), by using raw magic. Once he starts dueling with his father and they start pulling magic from the tower, well...
In Nightworld this is explained as being due to the Big Bad using magic to counteract the laws of physics. When he dies, nature reasserts itself and the underground cavern starts to collapse due to the weight of the ground above.
In Apotheosis, there is a peculiar example in which the boss is on the same side as the protagonists. The AI calling itself Tjaele Mosasa has been manipulating society for centuries to keep Bakunin a Stateless planet, and thus one that will tolerate Mosasa's existence. As soon as he's gone, the Proudhon Spaceport Development Corporation starts taking over, and the old society of Bakunin collapses.
In the Rainbow Magic series, in the final Sugar and Spice Fairy book, the return of all seven charms makes Jack Frost's Candy Castle collapse and melt away.
In "Rose", the Nestene Consciousness. When the anti-plastic hits, the facility goes ka-boom.
Justified in the Star Trek: Deep Space Nine episode "Extreme Measures," when Sloan dies, and it is feared that the resulting collapse of his mind-scape (which Bashir and O'Brien were exploring) would have been fatal to anyone still inside.
Criminal Minds: "Fisher King" (Part 2) The unsub blows himself up, forcing the team to first locate the hostage inside and escape while the house is burning.
BIONICLE put a unique twist on this by having the Big Badbe the Matoran Universe itself for the Grand Finale. This meant that if the villain died, the universe would fall apart and become uninhabitable. But there was another twist, namely that this process took about three days to happen. Everyone escaped within seconds, thanks to the writer taking artistic license with scale.
In Exalted, the Primodials have multiple souls organized into different Power Levels. The most important one is called the Fetich Soul, and killing it causes the Primordial to implode and come back wrong, with a new theme and powers.
In the Judges Guild adventure Dark Tower, the title building collapses after the lich Pnessutt is killed.
In the 3.5 Edition supplment Elder Evils, the Hulks of Zoretha cause the entire mountain in which their temple is located to collapse when they are defeated.
In the 1st Edition module S1 Tomb of Horrors, this happens when you kill the demilich Acererak. Except not really. You actually killed a fake and he has an illusion set up to make you think the dungeon is collapsing as a result and you get a fake map to another dungeon. If you go back after the collapse, you'll discover the ruse. The guy is kind of a prick.
At the end of Baldur's Gate II: The Throne of Bhaal the plane you're fighting on collapses shortly after the battle as the power that was sustaining it and that the Final Boss was channeling departs after their defeat. Unusually, you're at no risk having already left, but the boss, who wasn't quite dead, is crushed by it.
Justified in Call of Cthulhu: Dark Corners of the Earth, where defeating Hydra will make the psychic barrier she has raised around Y'ha'neth'lei to vanish, allowing the navy submarine to torpedo the place, unaware that there's someone inside aiding their efforts.
Dracula, in the Castlevania series, is a classic, and possibly the most famous, example of a Load Bearing Boss. When defeated, Castlevania, his lair, will almost always crumble, usually ending with the hero(es)/heroine(s) standing on a nearby cliff watching the castle fall. Possibly justified, as the two are mystically connected — doing it in reverse (sealing off the castle and then killing Dracula) is how Dracula was Killed Off for Real.
In Cave Story, beating the Final Boss will cause this, but beating the True Final Boss will stop it. The reason for this gets explained in-game: Ballos (the True Final Boss), whose powers are beyond his own ability to control, is actively tearing down the island. The Core (the Final Boss) is meant to seal him off and keep that from happening, so breaking the Core starts the fall. Killing the True Final Boss makes him stop tearing the island down, so it stops falling.
In Chrono Trigger, defeat of Magus and Lavos Core creates a time warp which consumes the surrounding environment. Also, defeat of Queen Zeal destroys The Black Omen. Thanks to time travel, you can actually do this several times.
Justified in the cases of Magus and Queen Zeal. Magus is attempting to summon Lavos to his castle to kill it himself, but the heroes interrupted him and Lavos basically yawned at them. When Queen Zeal is defeated, she calls upon Lavos, who disintegrates the Black Omen as he pulls you into his pocket dimension.
In Chrono Cross, defeating Miguel causes the time distortion in the Dead Sea to explode spectacularly.
In City of Heroes, this is revisited in the "Hess Trial", which references a lot of classic tropes. The final mission of a series takes place inside an active volcano, on dinky walkways suspended above a sea of lava, in which a Humongous Mecha stands ready for launch. The final boss, a cybernetically-enhanced army officer (and the only one capable of piloting the Megamech) causes the base to inexplicably self-destruct upon his defeat, prompting the involved heroes to flee with mere seconds to spare.
This is actually also very dangerous for groups that haven't done the mission yet, due to the way the game engine displays those type of messages. They jump onto the screen then fade out one at a time, and finishing the mission triggers a series of them: "Mission Completed!" "Badge Earned!" "Level Up!" "1:00 to escape!" "Enhancement Found!" Leading to memorable "Wait, what was that last one?" moments before a mad dash to the exit.
In DarksidersDragon/Straga is a load bearing boss. His death causes the Destroyer's Tower to fall. Except for its top. This was even lampshaded by Azrael.
The top of the tower still floating is stated to have only been due to its close proximity to the Destroyer himself.
All of the end-of-level bosses in Descent 1 and 2 - usually hostile reactors attempting to defend themselves by shooting energy balls, but sometimes there's a more traditional King Mook. Upon defeat, the countdown timer starts, a female Computer Voice announces the activation of the self destruction sequence, sirens start blaring, and the level is constantly rocked by tremors while the lighting blinks. The player must escape via the designated emergency exit within the designated time. If the player is successful in reaching the exit, a Cutscene shows your ship Outrunning The Fireballno matter how much time there is left on the timer. If the player fails to make it in time, the screen will Fade to White.
Zoma's case is a little odd, since later, in Dragon Quest I, Castle Charlock is still standing. Even if a new castle was constructed on the site, how would Dragon Lord have known the original layout given that he was a hatchling when it originally fell?
In Dragon Quest VIII, the Black Citadel starts collapsing after you defeat Rhapthorne. Interestingly, this is both foreshadowed and justified by a stone tablet found earlier in the dungeon, stating that the citadel cannot exist without it's master, and will "turn it's very substance against the pilgrims from the world of light" should he be defeated. In other words...No Ontological Inertia.
Played with in The Elder Scrolls III: Morrowind; the final boss, Dagoth Ur, is functionally immortal and, if killed, simply resurrects immediately and attacks you again, mocking you for thinking you could kill a god. When you destroy his Soul Jar, however, he becomes mortal; and when you finally do him in for good, large portions of his volcano base and the magical Humongous Mecha he was (re)building come tumbling down.
Justifiable in that it wasn't Dagoth Ur's death that caused the damage, but the destruction of a Cosmic Keystone. His death was just a side effect.
Played straight in Oblivion; when you kill Big Bad Mankar Camoran, his other-dimensional "Paradise" dies with him. But then, he did create it after all.
The Master from Fallout 1 triggers a bomb on a countdown timer that will destroy his base. You could also trigger the bomb yourself and run away cackling like a little sadistic schoolgirl as an alternative to dealing with the Master.
In Fallout: New Vegas: Dead Money, defeating Elijah causes the Vault to be rocked by explosions, as well as starting a timer on your bomb collar.
In the Old World Blues add-on, if Gabe is killed during the Residential Cyberdog Guard Test, you have ten seconds to leave the testing area before his atomic core detonates and incinerates everything in a 10-meter radius.
Often occurs around the middle of the game in the Final Fantasy series:
In Final Fantasy VI, defeating Kefka in his final form results in the collapse of his tower as the protagonists escape. Although, to be fair, the tower was made of magically combined junk and trash isn't known for its ability to hold together in a safe form all by itself. And killing Kefka causes all magic to cease to exist, thus removing the force binding the tower together. Tragically, Shadow chooses to stay behind and (presumably) dies in the collapse, vowing to start all over again.
Final Fantasy IX has an unusual twist on this trope; the Evil Forest that your airship crashes into after the introduction turns to stone after defeating its core. In a subversion, one of the Tantalus bandits doesn't make it out in time.
Played straight with Barbariccia and the Tower of Zot in Final Fantasy IV. Apparently, the tower was being held up in the sky by the Fiend of Wind's power, though it's not explained where the tower (or its remains) landed.
And again with the Giant of Bab-Il and the CPU.
Perfectly justified in Final Fantasy X: Yu Yevon is the summoner whose constant dream causes Sin to even exist; therefore, defeating him ends the dream and makes Sin dissolve into pyreflies.
Final Fantasy XIII gives us another justified example. Orphan, the fal'cie fought at the end of the game who is of a Big Bad Duumvirate with Barthandelus, is actually the power source of all Cocoon. When the protagonists kill it, the power system of Cocoon fails and it begins sinking towards Pulse.
Final Fantasy Tactics has this with its final boss battle. It's strongly implied that the heroes did not make it out, despite the ambiguous ending.
A variation: after the final battle in Grand Theft Auto: San Andreas (which is against a former ally who betrayed you, rather than against the Big Bad), the Big Bad shows up and then runs away again, stopping only to set some explosives that will destroy the building, giving you just enough time to escape. The mechanics of the mission fit this trope (you fight the Boss, then have to escape before the building is destroyed), but the explanation is different (in that there actually is an explanation).
In Great Greed, upon the defeat of Bio-Haz, his castle collapses and the heroes escape in a balloon. Shortly afterwards recurring boss Sarg is defeated, and his hideout collapses as well.
Half-Life 2. After you disable Dr. Breen's teleporter, it explodes in a reality ripping manner. However, it does this almost immediately afterward, leaving no time for escape. The only reason you survive is because of the GMan's timely intervention.
The Final Boss of the first game, the Nihilanth, is a spectacular example. Not only does its death cause the collapse of the chamber in which the player fights it, again escape only possible due to the GMan, but it rips open an entire dimension, causing the Earth to be subsequently ravaged by portal storms and allowing the Combine to transport enough of their military to conquer the planet in seven hours. Excellent work there, Gordon.
In Heretic, the Dome of D'Sparil magically shatters after the player defeats D'Sparil, and upon escaping the player is told he's escaped "mere moments" before its destruction. Though that's purely fluff. You can wait a couple dozen hours looking at the villain's corpse before stepping in the exit teleporter, and nothing will happen in the game. An actual in-game effect is that all remaining monsters on the level are instantly killed. But this doesn't reach too far because then you've got two more episodes (in the extended edition) fighting more of his monsters, eager to avenge their fallen master.
In The Legend of Zelda: Ocarina of Time, Ganondorf destroys the castle "with his last breath", perhaps out of spite, triggering a timed escape from the fortress. This also provides the location for the final battle against Ganon, on the ruins of the former castle.
Happens at the end of Super Meat Boy. Dr. Fetus pulls a Taking You with Me and activates the self-destruct system for his castle after plummeting to his doom, forcing the player to flee back to the start of the level in order to escape.
All of the Mega Man (Classic) games, though usually without the "escape the fortress" level.
A boss from the first Mega Man Zero game plays it straight. Thing is, fighting the Boss is the halfway point, and escaping from the Collapsing Lair is the second half of the level.
Mega Man X3 subverts this if you fight Vile in his factory stage. At the start of the fight, he says the factory is already set to destruct. Once you win, you always have about a minute to escape before the factory blows up.
Mega Man Battle Network 1, 3, 5 and 6 all end with the villain's real-world lair exploding after defeating the last boss.
Not a typical video game "boss" per se, but in the final normal level of MediEvil 2, Daniel must invade a giant cathedral possessed and haunted by demons, save 12 angels and use them to kill the head demon of the cathedral...doing so causes Dan to get no more than a minute to escape the cathedral, which is now absolutely annihilating itself, smashing to bits, and causing an explosion big enough to level that part of London.
Lampshaded in Double Dragon Neon when the space station explodes and crashes after you beat Mecha Biker. "I didn't know it was a load-bearing robot!"
Metroid is sometimes kind enough to have an explanation for the timer, initially using it for final bosses but lately just as often with the Warmup Boss instead.
In Metroid Fusion, there are two subversions, both in that the boss has to be defeated before the timer runs out.
First, the engines overheat due to the X-Parasites shutting down the cooling unit. You have five minutes to journey from Sector 5 to deep into Sector 3 to shut them down, and defeat a Beam Core-X inside.
Second, at the end of the game. You alter the orbit of the B.S.L Station, where it crashes into S.R.388, to vaporize both, and so destroy the X-Parasites inhabiting both. As you escape, you fight Omega Metroid, likely with about half your time gone.
The GBA remake of the first game, Metroid: Zero Mission, contains two. One is the classic Mother Brain, and the other is Mecha-Ridley, who sets the version-exclusive Space Pirate Mothership to self-destruct after being defeated.
In Metroid Prime 2: Echoes, there's two final bosses, one that's load bearing and one that you fight during the escape. Although if you want to be technical, it's actually Samus's actions after the boss is already dead that set off the planetary collapse.
In Metroid Prime (the first one) After you kill the Parasite Queen, she falls into the power core (or something like that) and causes the ship you're on to start falling apart.
Mother Brain, as pictured by Cracked in the page image. Twice.
Metroid Prime: Hunters includes an escape timer after every boss except the final. If you don't make it out on time, a wave of energy takes up the screen and you die. Unlike explosions revisited in other games, it does no damage to the surrounding area. Just made to break your suit, apparently.
Metroid II for the Game Boy avoided this trope; when you killed the Queen Metroid you simply had to make your way to the surface at your own pace and reenter your ship. Don't worry though, Samusgets to blow up the planet later.
Super Metroid makes up for it by slapping you with a timed explosion right at the start of the game, immediately after futilely facing the Warmup Boss Ridley, who killed the ship's crew and stole the baby Metroid.
Strangely enough, in Metroid Prime 3: Corruption, Samus herself gets a load bearing Hypermode when she lands on Phaaze. She has to not only FIND and KILL Dark Samus, but also Aurora Unit 313 before time runs out and she becomes wholly corrupted. The planet then explodes for completely unexplained reasons.
Dark Samus didn't read the Evil Overlord List. It turns out AU 313 was connected to the planet's core.
Metroid: Other M doesn't have a straight example, but due to a coincidence, Phantoon is one in terms of gameplay.
In No One Lives Forever, one of the encounters towards the end of the game, while not much of a boss fight, has a strong element of this. The vanquished foe has previously ingested a liquid, timed explosive, forcing Cate Archer to conduct a swift evacuation of the area in which the battle takes place.
After defeating the titular villain, Nemesis, in Odyssey: The Legend of Nemesis, his lair begins to self-destruct, catching on fire, and crumbling into rubble. A fitting and perhaps honorable coincidence is that while you are escaping his lair's self-destruction, "The Sunken Cathedral"by Claude DeBussy plays in the background (though it was played before confronting Nemesis), given that his lair is on an island.
Likewise, in Resident Evil 4, during your final battle with Krauser, he activates his time bombs, which only gives you three minutes to beat him and escape.
The final battle ends in you escaping on a jet ski while the entire island explodes as a result of Ada Wong activating the self-destruct mechanism. Lampshaded when Leon matter-of-factly tells his charge that they have to get off the island before it explodes (he's been in this kind of game before), and she answers "It's going to what?"
Every single Resident Evil game fits this trope. Whether the deadline starts before the boss fight or afterward, you can be sure the mansion/base/castle/ship/island will explode in the following cutscene.
In Ristar, the bad guy's fortress starts to explode as soon as the final blow is struck. However, the Big Bad seems to escape.
As Andross is defeated in the Star Fox series, the area in which the fight takes place explodes, forcing the player to escape. In 64, this is complete with Andross yelling, "If I'm going down I'm Taking You with Me!" At this point, James McButt shows up and you have to follow him through a maze to get out again — make a wrong turn and you'll get caught in the explosion.
Occurs several times in Breath of Fire I, and is played for tragedy once when Cerl combines High Heel-Face Turn with You Shall Not Pass, buying time for Ryu and the others to escape her fortress by fighting her former allies. Its disappearance confirms her death, and takes out another sympathic character in the process.
Defeating the Golden Diva in Wario Land 4 causes the golden pyramid to sink into the ground as Wario escapes with the treasure.
Syrup Castle in Wario Land 1 and 2 explodes after Captain Syrup is defeated, the first time being explained by a gigantic bomb being placed in the throne room, the second actually sending the boss flying into the horizon.
There's also Rollanratl in Wario Land: The Shake Dimension, who's a literal Load-Bearing Boss. He's actually holding up the boss arena ceiling, and once defeated the roof pretty much falls and crushes him.
Defeating Mundus in Devil May Cry causes the collapse of the entirety of Mallet Island.
Subverted in Sonic 3's Marble Garden Zone where the ground is destroyed by the boss BEFORE you fight him.
In Sonic And Knuckles, Flying Battery Zone has 3 bosses (most other zones have only 2), the second of which is more like an interactive cutscene than a boss. After said boss, the battleship starts to collapse and you have to get out. Justified in that it had fired lasers at a major support.
In Ico, the moment the final boss is killed, her entire castle, and the thousand-foot-high outcropping of rock it stands on, immediately crumbles into the sea for no discernable reason during an extended cutscene.
Subverted weirdly in Suikoden II: After defeating the final boss, the Beast Rune Incarnation, L'Renouille begins to rumble violently. Your hero is semi-literally dragged out of the throne room by one of his generals to keep from rushing into search for his "childhood friend" Jowy. Once the non-Timed Mission cutscene ends of everyone escaping... nothing happens to the castle and it still stands. However, the rumbling could conceivably have just been from the Beast Rune's unearthly death roar.
Even Shiro, the feral wolfdog, will convince the hero that he must flee. Somehow. With growling. Then presumably bites onto him and drags him out manually. Some characters do make a scene about the castle crumbling, making the fact it's still there after even weirder. (Maybe they didn't know? Wolfdogs just aren't good judges of falling architecture.)
The final boss of Suikoden I, Golden Hydra, which was Emperor Barbarosa transformed with the power of the Dragon King Sword. After the post-final-battle cutscene, Emperor Barbarosa leaps from the top of the castle and after a blinding flash of light and the sound of an explosion, the castle begins to collapse and the player must escape. Why the castle collapses is not clear; Perhaps the explosion was what destablized it (even though the explosion was on the outside of the castle, not inside), or perhaps the final boss's life was tied to the castle itself, much like Dracula and his castle in the Castlevania series.
The damage can't have been that extensive anyway, the palace is back in pristine condition as the home of the President a couple of years later in Suikoden II.
Happens yet again in Suikoden IV, to Fort El-Eal. When the final boss is defeated, its body begins to erupt in a series of explosions that start to bring the fort down. As the party escapes by boat, the entire fortress blows up in a tremendous explosion that would have wiped them out, were it not for The Hero's Heroic Sacrifice
In Quake II, after the final boss Makron is defeated in the level Final Showdown, the space station where it is staged blows up as soon as the protagonist, the Marine, escapes in Makron's escape pod.
Romeo Guilderstern in Vagrant Story. Since he had stolen the key to Lča Monde's power, and subsequently became its focus, his defeat ripped the Dark loose from the city's foundation. When Ashley inherited the Bloody Sin, he became the bearer of the Dark, and the ravage of time and decay that had been kept at bay for centuries suddenly swept into the ancient city.
The last boss of Neverwinter Nights 2 is holed inside an ancient ruin, which his destruction inevitably causes to collapse. Unusually, the game doesn't leave the player a chance to escape, but just cuts to the credits.
The expansion lampshades this, providing the above quote.
Ironically Jerro himself is guilty of this. He mentions after you defeat him that if he dies his Haven will collapse and everyone within will die.
There's a bit of an inversion in the original Neverwinter Nights expansion pack Shadow of Undrentide. The final Big Bad is being protected by the same magical artifact that is holding the floating city of Undrentide in the air. The only way to kill her is to first destroy the artifact, which causes Undrentide to start falling. You fight and kill her on top of the city while it's in freefall.
World of Warcraft has a bit of an opposite of this in Kologarn, 5th boss in the Ulduar raid instance. When you defeat him (being a giant with only his upper body in sight), he becomes the bridge to the next area.
Wording from a Titan computer in Northrend implies that the Old Gods are this for the entire planet. The reason the Titans sealed them away instead of killing them was because they were tied too much to Azeroth.
When The Sleeper is killed at the end of Gothic, his underground lair collapses around him — unfortunately, The Hero is still inside. (This does set him up nicely for a With This Herring moment in the sequel.)
In La-Mulana, defeating Mother causes the ruins of La-Mulana to collapse, which makes sense, since the ruins are the body of Mother, and the five-tier boss that you took down is her soul. Lemeza's escape happens in a cutscene in the original version, but the remake you have to play it out on a timer.
La-Mulana 2deconstructs this trope, with Lemeza on the run from Interpol as a result of the temple's destruction. Sure, he saved humanity from being destroyed and replaced by Mother, but who's going to believe that?
Averted in Tomb Raider 1 and Anniversary, where it's actually destroying the scion (load-bearing artifact?) that makes Atlantis collapse, and the fight with Natla is done while it is collapsing (Anniversary seems to be far less explicit about this for some reason). Played straight in Tomb Raider 2, where killing the Big Bad and getting the Dagger somehow makes a big portion of the Great Wall explode in the ending. Played straight again in Tomb Raider 4, as the great pyramid suddenly starts falling apart after Horus/Set is sealed, although in this case it's an important part of the ending.
Played in various ways (mostly straight) in Metal Slug 3. In the last level, a particularly large Mook Walker can only be fired upon from underneath; defeating it means you then have to avoid being crushed as its legs give out and its upper portion falls to the ground. One of the minibosses, a humongous, bolt-firing brain, brings down the house with its defeat. The rest of the level is spent escaping from the mothership as it collapses (harmlessly) around you. Then you fight the brain again, liberated, as it tries to Mind Rape you and your tank.
In Metal Slug 4, after you defeat Amadeus, you must escape his exploding base before you get engulfed in the explosion.
In Tales of Phantasia, huge amounts of energy unleashed during the battle with Dhaos in the Present causes the mausoleum where he was sealed to collapse.
On a lesser note, the first two times you take down a Desian Grand Cardinal, Raine activates their Lair's self-destruct system, destroying them.
Tekken 6: In Scenario Campaign, after defeating Azazel, you have to fight your way through mooks as the temple collapses.
Tenchu: Defeating the dark lord at the end of the game causes his evil lair to begin collapsing. This supposedly kills Rikimaru, until we learn in a later game that he escaped through a time portal into a futuristic world of technology. No, really.
Happens quite a lot in the Super Mario Bros. series (Bowser's Galaxy Reactor being a notable example).
From a gameplay perspective, it also happens toward the end of Mario & Luigi: Superstar Saga, after Cackletta's ghost is defeated. Storywise, another character had rigged Bowser's Castle with a Time Bomb. When you successfully flee on the back of a pterodactyl-like ally, the castle explodes in the sky.
New Super Mario Bros. Wii actually inverts this in the end, as a magically-enlarged (and quite angry) Bowser chases after Mario, ultimately resulting in him literally destroying the load-bearing pillars of his castle, causing it to collapse on him. Embarrassing!
After the Final Boss in the first Paper Mario, the castle begins to explode because the battle was so intense. Bowser's castle explodes right then and there in the sky while Peach's Castle with Mario and others are saved by the Star Spirits.
Happens nearly every time to King K. Rool in the Donkey Kong Country series, where Gangplank Galleon often sinks after he's defeated, and in the later games, as does the entirety of Crocodile Isle (in a way very much similar to Atlantis).
To be fair with Crocodile Isle, he was knocked into the island's core.
Happens with the final boss of almost every game in the Bomberman franchise, and sometimes the regular bosses as well.
In Portal, defeating the Final Boss causes the mainframe room to tear itself apart, catapulting you to the surface. This was given a The End... Or Is It? twist in a later update to set up the sequel.
In Portal 2, the Final Boss is an inversion. You have to defeat him to stop him from blowing up the facility due to negligence, partly because he's too busy trying to kill you to bother fixing the reactor.
In Life Force, after you destroy the heart of the Living Planet, the planet begins to self-destruct (or explode, hard to tell on 8 bit games). Cue the high speed escape through closing gates that has surely resulted in many a broken controller lodged in many a TV screen.
The rest of the Gradius series does this too, with the escape being a short cutscene... unless you're playing the arcade version of Gradius III, in which case you get a high speed chase through the hardest fucking section of the game.
Stargate for the Genesis/Mega Drive and SNES has Ra's pyramid explode after his defeat because O'Neil activated the nuclear bomb the team brought with them to explode and teleported out just before detonation.
Vandal Hearts 2; possibly justified in that the final boss had done extensive damage to the building in transforming to his One-Winged Angel form.
This happens in Phantasy Star IV fairly often: killing Zio destroys his fort, killing Lashiec destroys the Air Castle, and killing Dark Force Number 2 destroys the Garuberk Tower (though that last one may be justified, in that the Garuberk Tower is actually part of Dark Force's physical body.)
Masterfully subverted in Phantasy Star III, where it's actually you that causes the final dungeon to blow up after beating the boss.
In X-Men 2: Clone Wars for the Genesis, defeating Master Mold in the Sentinel Factory level causes the whole place to blow up. In an interesting Chekhov's Gun moment, you might notice an emergency exit shortly before fighting the boss. This is the only way you can actually leave the place before goes sky-high.
You bring down Mother's lair on top of her (while apparently unkillable conventionally, this must not apply to being crushed to death) by attacking the load-bearing pillars in her chamber.
Similarly, the Lotus Assassin fortress mostly seems to collapse because of the rogue golems (and to some extent, Death's Hand) damaging the structural supports, rather than your defeat of Mistress Jia.
You fight the Emperor and the real Big Bad in a floating castle powered by magic. You'd think it would fall out of the sky afterwards, right? It doesn't.
In Doom II, killing the final boss (on level 30) causes zillions of massive explosions to erupt all over Hell from the boss's death throes. In the words of the game, "Hell is a wreck."
In Persona 3, defeatingNyx and sealing her away causes Tartarus to get pulled up into her physical manifestation, the Moon, returning Gekkoukan High to its form of an ordinary school campus.
Killorn Keep in Ultima Underworld II can be crashed by killing the two brain creatures in a hidden room underneath. The world isn't actually destroyed until you leave it and re-enter. All the keep's residents die, which renders the game Unwinnable if you do it too soon.
Magi-Nation, though somewhat justified as the Big Bad's presence and power are what cause the place to exist in the first place.
It's also worth noting that this is a rare example of a load-bearing Bonus Boss.
Potentially subverted in the first game, where after defeating Drek, his Deplanetizer is flipped upside down, allowing the heroes to destroy his planet. Doing so causes a rain of flaming rocks, however, requiring Ratchet & Clank to get out of there.
In Resistance 3, the final challenge of the game is literally destroying the power rods and, in turn, the supports to the Chimeran Tower in New York, so... you kind of get what you expect there.
Wonder-Jergingha in The Wonderful 101. Once he's destroyed, the massive fortress begins to break apart... Once you escape, however, Wonder-Red realizes that what they escaped wasn't the GEATH-Waksay breaking apart, nor was Jergingha destroyed; upon his defeat, he decided to transform into his final form, and they were just escaping before he changed form with the Wonderful Ones still inside.
Defeating the final boss of a particular level of Mass Effect 2 causes the level (a derelict starship) to crash into a brown dwarf. This is justified in-game since finishing the boss fight requires the player destroy the primary component of the ship's propulsion system, which had been keeping the ship from falling into the brown dwarf in the first place.
Endgame spoilers: when you defeat the human-Reaper larva, it knocks the platforms you're standing on down as it falls. While Shepard survives the fall, his squadmates will only survive if they're loyal.
Subverted in the Collector Base itself, where Shepard destroys it by sabotaging the reactor, creating an explosion that either destroys the base completely, or just destroys all life-forms in the base.
The Water Guardian in Brave Fencer Musashi is holding up the roof of the battle area.. Somewhat subverted, in that, while you can't return to the room you fight the boss in, the dungeon overall is still possible to return to.
In the Teenage Mutant Ninja Turtles games from the '80s and '90s, the Technodrome, Krang's Spaship, whatever the final base is, it's guaranteed to explode upon knocking the Shredder unconcious. There is absolutely no ingame explanation for this—though a Kill Switch of some sort is the most "logical."
Demonic and Flameye in Purple, once killed, destroy their fortresses, forcing the player to reach the question mark orb in time.
In the Revenge Of Meta Knight subgame of Kirby Super Star, every time Kirby defeats a boss, a part of the Halberd explodes. These are sort of understandable, most of the bosses are machines that are parts of the Halberd itself. Except for one. When you defeat Mr. Frosty on one of the wings, the area explodes for seemingly no reason. And Kirby just stands there in the explosion, totally unfazed.
Summon Night 2 plays with the trope: A 'professional treasure-hunter' muses that he's encountered many a load-bearing boss in his time, but there turns out to be no such thing.
In M.U.S.H.A., after defeating the Final Boss, this message pops up: "You've destroyed their main base! Escape before it blows!" Escape is automatic, but not without showing some damage.
Legacy of Kain: Happens to the Sarafan when they sort-of-kill Janos Audron. Lampshaded with "The fiend intends to bury us alive!".
The final boss of The Legend of Dragoon is a spectacular example of both Load-Bearing Boss and Defeat Equals ExplosionThe explosions of his defeat set off a chain reaction that destroys the entire moon. The load bearing portion of this trope can be justified however, since he had actually fused together with the core of the moon itself. The cause of his explosion however is not entirely clear, but it was most likely the vast amount of magical energies in his body going out of control upon his death
Kid Icarus: Uprising: Several chapters' levels start to fall apart upon defeat of the boss. This includes chapters 8, 9, 12, 13, 14, 15, 16, and 17. It's even Lampshaded by Hades at the end of chapter 14.
Hades: This place is going to the dogs without Phosphora around!
Once Bork (he's a Big Ork) is defeated in RuneScape rocks will start falling from the roof of his cave, squishing the player dead if they don't collect their loot and teleport out fast.
In EarthBound, defeating the Mani Mani Statue ends Moonside and Monotoli's popularity. Averted later with the Starman DX; while the Stonhenge Base isn't destroyed, all the enemies vanish, along with the Sword of Kings, Poo's infamous Infinity+1 Sword. The instance with Moonside is repeated with Magicant, where defeating Ness's Nightmare, embodied as the Mani Mani Statue, causes Ness to wake up and Magicant to fade.Mother 3 had Mr. Genetor as a load bearing boss, as his defeat causes the Thunder Tower to shut down and closes the area off forever. The final boss plays with this. You beat him, nothing happens. Then you go and cause an apocalypse yourself immediately afterwards... sorta. It's more like world rejuvenation.
Red Falcon in Contra III: The Alien Wars and the Relic of Morai in Contra: Shattered Soldier.
XCOM: Enemy Unknown. Most people wouldn't think it but this fits the trope. the last level takes place on a giant enemy ship that is somehow controlled by the Uber Etherial (the final boss). When the player kills it a cutscene triggers and the ship begins to collapse into a black hole. All but one soldier run away and escape the ship before the one soldier (the Volunteer) stays behind and takes the ship into space to blow it up before it collapses.
Defeating MTHR in Dino Crisis 3 causes the Ozymandius's self destruct sequence to activate. Justified, as the ship was designed to self-destruct should the MTHR System fail.
In Space Quest II, Vohaul's asteroid base goes into a decaying orbit after his death. In III, destroying the Stealth Field Generator on Ortega sets off a series of catastrophic volcanic eruptions that will kill Roger if he fails to escape in time.
Played straight in Ape Escape 2. As soon as Specter is captured, his Moon Base explodes for no apparent reason.
Legend of Legaia is in love with this trope. Near the beginning, defeating the Golem boss causes the cave you are in to collapse. The cave was already unstable beforehand though; the battle just shook things up a bit too much. Later on, Zeto's Dungeon collapses after defeating the titular boss. This is a bit of a strange case as the dungeon is not actually shown to collapse, but if you return to it on the world map, you'll find it "crumbled" and cannot enter it. Subverted later on in Zora's Castle, when Songi shows up after you defeat Zora, and destroys the mist generator which keeps the castle afloat. The inevitable happens afterwords. Happens yet again with the Rogue boss; Rogue's Tower begins to break apart as soon as it dies. Yet another example is Cort in Jette's Fortress. After being defeated, the Mist Generator self destructs and the fortress begins to crumble shortly after. He actually explicitly states "The mist generator and I are one. If I die, the mist generator dies..."
He actually gets to be a load bearing boss TWICE, when he re-appears as the final boss. When Cort fell and "died", he was actually consumed by Juggernaught, and proceeded to merge with him. Later, Juggernaught assimilates itself with Rim Elm, the starting village, turning into the final dungeon, and a Womb Level to boot. After travelling Juggernaught's guts, you face Cort one last time at the heart...which he is actually contained in. He destroys it when he bursts out to fight you. Guess what happens to Juggernaught's body after the battle?
Probably justified; Neo Bowser Castle was created from a wish that Bowser made upon the Dream Stone. Therefore, the castle is most likely tied to the power of the stone itself, and it's destruction upon Dreamy Bowser's defeat caused the castle to perish along with it.
In the Xbox exclusive Breakdown, Site Zero starts collapsing after you destroy Nexus. It's not necessarily a "boss" per se, (Though earlier, you do fight it's "avatar", Solus), but it is still a sentient being you must kick and punch into oblivion, so it fits for this trope. It's also probably justified, as Nexus was stated earlier to be Site Zero's control center.
In Ducktales Remastered, defeating Dracula Duck causes Mt. Vesuvius to erupt.
In Mighty Morphin' Power Rangers: The Movie Edition for SNES, defeating Ivan Ooze causes his base's self-destruct system to activate, and the player has 99.99 seconds to escape.
Gameplay-wise, Doc-Ock and Carnage from the first PS1 Spider-Man count as this. However, the underwater facility's destruction is not due to their defeat, but rather a pressure build-up which resulted from you sabotaging the facility's fog-producing surface vents. It had just hit critical point upon their defeat. Cue final escape level filled with explosions and a nigh-unstoppable Ock-Carnage fusion on your tail.
Inverted in Xena: Warrior Princess with the final boss fight, where you must lure the boss into destroying several support pillars to collapse the battle arena on top of it...and you too, if you don't run to safety fast enough.
In Alundra2, you have 3 minutes to escape the flying fortress after defeating the final boss.
Rogue Galaxy has the Demon Battleship, which falls into a volcano and explodes after being defeated, resulting in a chain reaction that turns the whole region into a sea of lava within minutes. The party just barely escapes in time.
In one early mission in Grandia the party must enter a mine and beat the Orc King there. Once you do the entire mine collapses for no apparent reason.
In Wild Arms and it's remake, Alter Code F, the Ghost Ship sinks after defeating Captain Geist. In the original, nothing happens right away, and it only sinks once you leave the dungeon. However, in the remake, the dungeon begins to collapse as soon as you defeat Geist, and you're given an overly-generous 15 minutes to abandon ship.
Inverted at the end of Parasite Eve, where YOU blow up the final area in order to kill the last boss.
The rather tongue-in-cheek Dungeons of Kong has a load-bearing boss known only as the "Ancient Evil."
The last dungeon in Threads of Fate collapses after you defeat the final boss.
The final dungeon in Bravely Default collapses in both the true and false ending, after defeating their respective final boss.
The final mission of Star Wars: Starfighter has you chasing the final boss through the interior of a Droid Control Ship. When you finally take him down, the DCS starts to blow up for no explained reason. Though it was probably due to accumulated damage to the ship over the course of the mission, the way it occurs fits with this trope.
In The Longing Ribbon, the mansion in which the game takes place begins to collapse once the final boss is killed, and you have just over a minute to escape.
The final boss of Headhunter: Redemption, a computer chip heavily protected by several defense mechanisms that must be bypassed before being destroyed. Justified in that it controls all functions of the facility, and is essentially a Reactor Boss.
Candy Floss earlier in the game may also be one. Some tremors occur shortly after his death, though it is not made clear if this is the area self-destructing, or if something else is occurring. There are a few more tremors in another cutscene shortly after though, as Jack and MW 3 M leave the area, so it's probably safe to assume the place was coming down.
Invoked in the Webcomic Casey and Andy: Quantum Crook holds sterotypical Evil Overlord Mulligan as hostage to cover his escape. When the confused main characters ask why they should care about him killing their archnemesis, Quantum Crook explains this trope to them.
The Adventures of Dr. McNinja: Inverted — an ancient robot which must be defeated at tennis once a year (don't ask) breaks apart when the main character fails to defeat it; the temple housing it begins to collapse shortly thereafter.
Homestuck. Snowman is pretty much the ultimate example: if she dies, the entire universe goes down with her. She uses this fact to torment Spades Slick without fear of retrubution, as nobody dares lay a finger on her.
She is eventually killed though, thanks to Doc Scratch's schemes.
Invoked in the famous Overlord List, where it is pointed out that, even though the Evil Overlord should intend to live forever, buildings should always be reinforced, just in case.
Referenced on Homestar Runner, in Strong Bad Email #173, "the paper". Strong Bad is seen on a sinking island, and says to himself "How is this island sinking? I didn't even kill any end bosses!"
Homestar Runner also parodies it in Thy Dungeonman where, if you try enough times, you can actually "get ye flask", only to be told that it was a load-bearing flask and picking it up caused the dungeon to collapse on you.
This is referenced again in the final episode of Strong Bad's Cool Game for Attractive People. After finally defeating Ultimate Trogdor, the dungeon begins to collapse. Homestar comments that he "must've been a load-bearing dragon."
In the Forum Community/MMORPG Gaia Online, one NPC builds an enormous tower that inexplicably collapses after he is shot from miles away by a Black Cloak Sniper. Like most of the Gaia Online storyline, this didn't make much sense, but looked really cool.
Played with in the Whateley Universe. It's well known that Karedonia (a small island in the Caribbean enlarged by deliberate volcanic eruption) has a very unstable volcano under it, and the only thing that keeps it from blowing up is the beating heart of King Wilkins (also known as the supervillain Gizmatic).
Played with in Kim Possible with the many, many lairs that get destroyed; once even Lampshaded when Kim states that she wishes just once that the bad guys' lair wouldn't blow up.
Jackie Chan Adventures: In the first Season Finale, Shendu magically restores his old palace as he prepares to release an army of dragons. Once he's beaten, the palace crumbles back into dust, along with the treasure the Dark Hand guys wanted.
In the Aardman short film Stage Fright, after the villain kicks the bucket (literally and figuratively), the theatre starts collapsing.
In The Last Unicorn, after the defeat of the Red Bull, King Haggard's Castle crumbles, throwing him into the sea.
The Powerpuff Girls episode "Knock It Off" has Dick Hardly's lair collapsing as his Powerpuff clones turn on him, with one of them telling the Professor to get him and the girls out before it's too late.