Old-as-dirt children's anime Doraemon featured a device called the What If Phonebox, a telephone booth that would transport the occupants to a dimension with the specified What If. (Do the Doctor and Bill and Ted know about this?)
One chapter of Angel Sanctuary featured Setsuna in a Lotus Eater machine where there was no... trouble in heaven, Sara wasn't his sister but is girlfriend and Kira was his kind and clever sempai that tutored him. He decided that the real world needed him.
The 9th One Piece movie use this for the basis of "Episode of Chopper". Which is a retelling Drum Island arc with a few differences in the cast (No Vivi, Franky and Robin are, who didn't join the crew at that point, were there), the crew already having the Thousand Sunny as their ship opposed to Merry, Wapol having a brother, etc)
Evangelion ANIMA is an Alternate Continuity take on Neon Genesis Evangelion, the point of divergence being End Of Evangelion, where the JSSDF sides with NERV instead of SEELE, helping them fight off the Mass Production Evas and avert Third Impact. The story picks up three years later, where NERV, now under the command of Misato, is a much more benevolent organization, and the Eva pilots have had three years of relative peace in which to grow up and (somewhat) deal with their personal issues.
The Full Metal Panic series happens in a scenario where Mikhail Gorbachev was assassinated by terrorists and, as such, his political restructuring plans never came to pass, the URSS still exists, and the world is still entrenched in the Cold War up to the present day.
The Doctor Who: Unbound audio dramas sometimes take the Elseworld approach and sometimes the Alternate Universe approach. Or, seemingly both, or neither. All except one dealt with non-Canon Doctors. They ranged from "what if the Doctor and Susan had never left Gallifrey?" (Auld Mortality) to "what if the Doctor had not been UNIT's scientific advisor?" (Sympathy for the Devil) to "what if the Doctor had escaped the justice of the Time Lords at the end of The War Games?" (Exile, with a cameo by the Nicholas Briggs Doctor), "what if the Valeyard had won at the end of The Trial of a Time Lord?" ("...He Jests at Tears"), to "what if the Doctor believed that the ends justified the means? (Full Fathom Five) to Deadline, set in a reality where The BBC decided to make a 1960s television series called Doctor Who... but it failed and never got even as far as the Pilot Episode stage! (Apart from that it has Magical Realist elements, too.)
Which is to say nothing of the expansion set that "What If Week" was promoting. Called Planar Chaos, it was about alternate dimensions/realities, both in terms of alternate story history creating cards like the white "Crovax, Ascendant Hero", the black "Mirri, the Cursed", and the red "Akroma, Angel of Fury", as well as off-color versions of well-known cards, shifted into colors that share or better fit the existing stats and abilities, creating the likes of Serra Sphinx (a blue Serra Angel), Bog Serpent (a black Sea Serpent), and Fa'adiyah Seer (a green Sinbad).
Various cases included "What if Gwen Stacy survived", "What if The Punisher received the Venom symbiote" and "What if every member of the Fantastic Four received the same power" to "What if Wolverine ended up in the Conan universe", "What if Aunt May was bitten by the radioactive spider", "What if Galactus was Ben and May's nephew" and, of course, "What if Magneto, Iron Man, Colossus and Dr Doom got stuck in the same elevator"?
Later What If?s from Marvel have pretty much ditched the absurdist (or at least gag-inducing) settings for more plausible alternatives, for example "What if Captain America had won the Civil War?" or "What if the Siege of Asgard had been successful?"
Indeed, although some of the more funny ones stick in fans' minds the most, it should be noted that the overwhelming majority of What If? stories played things very straight. Also, quite a lot of them ended unhappily, leaving readers with the Panglossian aesop that the mainstream Marvel timeline is the best of all possible Marvel Universes, as more often than not changes that at first glance seemed positive or indifferent could result in the End of the World. This became quite anvilicious in a What If? published concurrently with the wedding of Jean Grey and Scott Summers; it contained two stories where Jean hooked up with people other than Scott, and one where Scott and Jean got married much sooner. All these couplings had a negative impact, and one of them indeed ending with the Phoenix destroying the universe.
An actually quite nice one was "What if Dr. Strange had been a disciple of Dormammu?" It goes into great detail about Dr. Strange's self-centeredness ("No more patients today, I'm reviewing my stock portfolio!") leading to a career in evil, but shows that ultimately he would have chosen goodness and become just about like he is today.
And then there was a tragic one after Avengers Disassembled containing a What If? within a What If? — where Captain America and Wanda were insane but in love, and if the Avengers had not interfered they would have both regained their sanity and made a much better world. (As it actually happened, they killed themselves).
Star Wars: Infinities is a series of one-shot comic issues built around this concept. Two examples include Luke dying on Hoth and Leia having to take up his mantle as well as her own, and C-3PO getting blown to bits in Jabba's palace... which somehow results in Darth Vader getting returned to the Light Side of the Force without dying.
The 'what if?' for A New Hope is the craziest. The lynchpin for the change is Luke failing to destroy the original Death Star, with the rest of the story switching between bizarre events such as Leia becoming an obvious visual reference to an SS officer after falling to the dark side and the Death Star being renamed the "Justice Star," to "alternate" scenes that are really just copies of actual canon scenes from the movies with characters switched around, one of which even has Luke learning Vader is his father and saying the exact same line in response. The story ends with what one review describes as "Cosmic 9/11;" seriously, you have to see it to believe it.
And the Return of the Jedi Infinities book, where Leia goes to the Death Star too, Han ends up permanatly blind, the Emperor escapes despite Vader's redemption, and the scene everyone remembers—redeemed Vader in white armor.
There's even official toys of that last one.
DC Comics was doing these type of stories years before Marvel, but they called them "Imaginary Stories." In later years, the name "Imaginary Story" came to viewed as corny, so DC took to calling them "Elseworlds" stories, instead. The Elseworlds tales more frequently focused on plunking the characters into a different setting, rather than changing a historical incident, but some like Alan Davis's The Nail do take the classic, well, For Want of a Nail approach.
This is pretty much the driving force behind most fanfics.
Crisis: What if in the episode Exile, Kal gets mad enough to rape Chloe rather than just throwing her out of his apartment? A Dark Fic is what you get.
Wounded Heart: What if in Abyss, Chloe finds out Clark mind-wiped her?
Downfall works on this premise, messing freely with everything, while explicitiely keeping eveyone within their canon character constraints. Aizen is a plotter. Unohana is Team Mom... and she kills people with her bare hands
John Biles' Ranma 1/2: Elseworlds (sadly on extended hiatus) explored variations such as "what if Ukyo stayed together with Ranma from the start?" to "what if Akane went to Jyusenkyo instead of Ranma?" to "what if the story takes place in the World Of Darkness?"
There had been a few fics in Axis Powers Hetalia asking what would have happened if the Americans didn't win the American Revolution.
The Fruits Basket fanfic "Eyes of the Cat" is solely dependent on the premise that Kyo, as the cat of the zodiac, may be able to see ghosts.
The Alternate Universe FicNed Stark Lives, which is about Eddard Stark being allowed by Cersei to take the black instead of being executed by her insane son. Despite the War of the Five Kings being more or less averted by this change, the story is just as violent as the original series.
In the Total Drama Island story Legacy, the climactic encounter with the chainsaw psycho (Episode #19, “Hook, Line and Screamer”) turns out differently than the canon version. That single change drives the entire story, with consequences that are still felt a decade later.
The main plot of Donnie Darko is essentially a few days of a "What If" scenario for a handful of people, eventually ending by returning where the tangential universe started in the first place and avoiding the "What If".
Although the film doesn't actually explore possible historical consequences. The answer to "what if" is: then Hitler would get killed, and the movie would end soon after.
The Animorphs book Back to Before has a battle-weary Jake ask "What if we never walked through the abandoned construction site?" Some of the results are amusing, such as Marco and Rachel going out on a date, but others... Well, just because you don't become the Animorphs that doesn't mean the war doesn't happen.
Also: What if the kids gave up? Earth becomes a Yeerk-infested hell, as you might expect, with the kids themselves becoming Controllers.
What if Jake became too ruthless and cocky? In #41, Jake, in the heat of battle, leaves Marco and Rachel to fend for themselves, in order to save the rest of the team. The continuation of this mindset is shown in the far future: Tom suspected Jake of being an "Andalite bandit", and turned him into a Controller. Ax, Marco, and Cassie are taken, Rachel is gravely wounded in the ensuing battle, and Tobias escapes. Marco becomes host to Visser Two, and Ax becomes a key player in the attack on his homeworld. Cassie's Yeerk, Niss, joins the Evolutionist Front, a terrorist group dedicated to the creation of artificial hosts, led by Tobias, who permanently morphs Ax. But even Cassie and Tobias aren't good guys: Cassie becomes ruthless, cynical and practically evil ("In a war, Jake, anything is justified."), and Tobias is completely willing to let Cassie die to score a victory ("Save one, or save many? The choice wasn't so hard at the Ragskin building, when you left Marco and Rachel to save themselves.")
Older tropers and ones who frequent used bookstores may be aware of a Sci Fi pulp magazine titled "if: Worlds of Science Fiction".
World War by Harry Turtledove asks "What if World War II was interrupted by an Alien Invasion?" His other main series, Timeline-191, is based on the more conventional question, "What if the south won the American Civil War?" while his earlier novel Guns of the South poses, "What if a racist group from South Africa in the near future travelled back in time to supply the Confederacy with AK-47s?"
"What if"s are basically José Saramago's source of inspiration. "What if people suddenly went blind?", "What if nobody died?", "What if everyone cast blank ballots?", etc. He mostly uses these to make comments on society and politics.
A series of essays by eminent historians is entitled simply "What If". It includes topics like "What If the Americans lost the Revolution?" and "What if Pontius Pilate spared Jesus?"
Discussed in the Iron Man 2 novelisation, where Tony suspects that being brought up by an alcohol-and-rage-fuelled father in Siberia would have caused him to turn out like Ivan Vanko.
Vladimir Vasilyev's novel Wolfish Nature and its sequel The Beach in Each of Us explores a world where humans have descended from dogs instead of apes. For simplicity, the author keeps many geographical names (e.g. continents, cities, countries) from Real Life, and many character names are also similar to Real Life names. Unlike us, the species canus sapiens sapiens have made incredible advances in bioengineering, culminating in the Bio-Correction during the 18th century, which removed the "Wolf Gene" (which allows one to kill another person) from the entire species. As such, wars are replaced with spy games on a grand scale. Murder is such a rarity that ordinary cops aren't trained to catch killers (all of whom are psychopaths anyway). Special agents can be trained to kill, but have to spend months in psychological recovery after the fact. Biotechnology is everywhere, although "dead" technology is slowly starting to replace it. The first novel kicks off with the discovery of an isolated enclave of unmodified people (i.e. they still have the Wolf Gene) in Siberia. The wolves immediately kill the person who exposes them and go after anyone in his address book, as he made a call shortly before being killed. However, the world governments quickly find out about their existence and send agents to Siberia. After all, any country can use the active Wolf Gene to breed an army of merciless soldiers. Instead of the concept of race, the dog-humans' "morphemes" (i.e. breeds) are often mentioned in descriptions.
Martin Cruz Smith's The Indians Won postulates that after gathering together to fight and win the Greasy Grass (Little Big Horn) battle, the Great Plains nations decide not to split up and go home. Instead, they stay together and draw the attention of European investors, who provide them with the supplies they need to withstand Manifest Destiny. This attracts other tribes to join them, at last forming the United Indian Nations. The U.S. is finally forced to capitulate and cede to them what would have become the Midwestern and Great Plains states from Canada to Mexico. So now you have East USA and West USA and a nice big Indian Nation at the center.
Fatherland, a 1994 TV movie on HBO (based on the novel by Robert Harris), set in a 1960s Germany in a timeline in which Nazi Germany more or less won World War II and got into a Cold War with the US while fighting a guerrilla war with a remnant of the Soviet Union.
Heroes asks, "What If... there were people with super powers running around in the real world?"
The Doctor Who episode "Turn Left" presented a world where Donna never met the Doctor, and humanity was more or less screwed.
And the Doctor Who spinoff The Sarah Jane Adventures has a storyline asking "What if Sarah, rather than her best friend, had died in an accident as a teenage girl?"
Are You Afraid of the Dark?: Members of the Midnight Society (the original one, anyway — before the show jumped the shark) frequently included a "What if" question when introducing their story, i.e. "What if you found out the future held something incredibly evil, and there was nothing you could do to change it?"
Even if not the premise of a series, what-ifs can be used to carry a single episode's plotline. Example, "The One That Could Have Been", Friends.
NewsRadio had two of these episodes, both with an opening introduction by Phil Hartman:
What if the show took place on a space station and reported the "space news"? ("Space")
What if the show took place on the luxury liner called Titanic? ("Sinking Ship")
The BBC-made series If... was a serious docu-drama take on What If,'documenting' what might happen in Britain should some issue of the time become reality e.g. oil running out,blackouts or legalising drugs.
Buffy the Vampire Slayer episode "The Wish": what if Buffy Summers had never come to Sunnydale? The answer: a lot of really bad stuff.
Perhaps the most successful example of this trope is the Star Trek: The Original Series episode "Mirror, Mirror", which formed the basis of episodes from all of the subsequent series except Next Generation and Voyager... but they got theirs in a novel (A Mirror Darkly).
The "What if?" question being answered by that episode was, of course, "What if Spock had a goatee?"
Sliders used this trope as its main premise: "What if antibiotics had never been invented?" "What if America had lost the Cold War?" "What if traditional gender roles were swapped?" and so on.
One episode of Friends ends on a What If note. Joey, Chandler, and Monica imagine what would Joey and Monica's lives be like if Monica married Joey instead of Chandler. It shows a very obese Joey in Monica's apartment sitting down to a really huge dinner prepared by Monica, who was more than happy to make all the food for him. The episodes ends with the fat Joey saying his famous "How you doing?" catchphrase to a piece of fried chicken before he eats it.
Not to mention a two-parter for Friends (fittingly titled "The One That Could Have Been") which showed an alternative history for the group if 1) Ross hadn't discovered his wife was a lesbian 2) Rachel hadn't walked out on her marriage 3) Joey had remained on Days of Our Lives 4) Monica was still fat 5) Phoebe became a stockbroker 6) Chandler walked out on his job.
Trance of Andromeda has this as her superpower, basically seeing future possibilities and trying to steer the present toward the "best" one. She also prunes a bonsai quite often.
An episode explores what would happen if Rhade killed Dylan at the start of the Nietzschean rebellion instead of the other way around. While Rhade would still try to re-create the Commonwealth, his efforts would be futile, costing him many allies. At the end, he realizes that Dylan is a better candidate for this, goes back in time, kills his past self, and throws the fight with Dylan, leading to the series' timeline.
Party of Five's 100th episode entitled "What If" had Bailey in a coma where he imagined an alternate reality where his parents had never been killed in the car crash.
Among the alternate stuff: Julia's kind of a bookworm while Claudia is kind of a slut
Various alternate realities presented in Stargate SG-1 tend to have major changes resulting from Sam Carter not being in the military, among other things.
In Farscape John gets to view a bunch of "What if?" realities in the episode "Unrealized Reality", then has to figure out how to navigate his way back to the right one to avoid any of the "ifs" becoming permanent. When the gang goes to Earth in the past in "Kansas", John tells his friends that they have to save his father so he will be inspired to become an astronaut and go on to meet all of them.
During a production meeting for Felicity, J. J. Abrams off-handedly asked "What if Felicity was a secret agent?" to try and develop a plot with relatively higher stakes. It was a joke, but he'd eventually answer the question with Alias.
Both JAG and its spinoff NCIS did episodes that revolved around the main characters making different decisions (or events that occurred one way in the "prime" timeline happening the other way). The JAG episode was even titled "What If?".
Bewitched once explored the possible consequences if Samantha had admitted her powers to Darrin before he asked her to marry him.
Xena: Warrior Princess: The fates once showed Xena how things would be if she never killed anyone. They did by placing her in such a timeline on the proviso that, if she ever kills anyone in that new reality, she'll return to the original. In the new reality, she was still living in her home village, her younger brother was still alive, her engagement was still on. The first downside was her mother no longer being alive. Then she learns of the consequences of her not doing the good things she did as The Atoner in the original timeline. The last drop was Gabrielle becoming a ruthless killer to escape a life of slavery. That was the Berserk Button that made Xena decide to return to the original timeline.
Karzahni of BIONICLE actually has "What If" as a superpower; he can give people visions of possible past or future outcomes. He tends to use this as a psychological attack, showing "What if you didn't survive that situation?" or "What if you couldn't save that guy at that crucial moment?" It's rarely pretty... and when it is pretty, it becomes a Lotus-Eater Machine.
One character then manages to use it against him, by daring him to show them what would happen if the Great Spirit dies. When he does so, he finds out that the answer is "the end of the universe," and that he's not nearly as important as he likes to think. This revelation causes him to go BSOD.
In Red vs. Blue, Church tries to take advantage of this trope to change the future (What if Donut didn't kill Tex? What if Captain Flowers hadn't died?). Unfortunately... it didn't work out so well. In fact, trying to change the past ended up causing all the things he was hoping to avoid to happen anyway, including his own death.
!HERO: The Rock Opera is this for The Bible: What if Jesus was born in Bethlehem, Pennsylvania? And moreover, what if Jesus wasn't born until the modern times?
For January 2012, Sally Forth did a storyline where Ted uses the 2012 Mayan prophecy as a reason to look back on their lives, which lead to a two-week bit where they show what life would be like if Sally and Ted had never met.
An ongoing project is the Dornian Heresy. The trope is somewhat subverted, since rather than one point of divergence, there's actually several, but the spirit of the trope is still there. The premise: What if Warmaster Horus had not fallen to the powers of Chaos? Though rather miffed, the gods turn to Plan B: turn Rogal Dorn of the Imperial Fists instead. What then happens is a very odd mixture of Bizarro Universe and Mirror Universe (while some things stay the same, adding to the oddities). Here's just a few of the changers:
The World Eaters under Angron become the paragons of martial honor and virtue, and are by far some of the most well regarded of the Emperor's Space Marine Legions (yes, legions).
The Emperor's Children are still stuck up snobs, but they're perfectionists whose hearts are on the Imperials' side.
The Space Wolves have dedicated themselves to Khorne, and are now both figuratively and literally Ax Crazy.
The White Scars are so obsessed with speed and thrills while worshipping Slaanesh the Speed Freakz of the Orkz would be envious.
The Word Bearers are the priesthood of the Imperium and use their knowledge of the Warp to exorcise daemons instead of summoning them.
The Thousand Sons have renounced sorcery and become one of the most loyal Legions of the Imperium, and Magnus is the advocate and spokesperson for psykers everywhere.
Abbadon STILL hates Horus for being weak and a fool, and reorganizes the Sons of Horus into the Black Templars.
Its story also presents another question: "What If... people were already aware of demons before the start of Shin Megami Tensei?" The answer isn't provided until the Devil Summonerprequelgames: "Thor would have been killed before he launched the nuclear missiles, instead of after, averting the main-series apocalypse and leading to a very different world." The Persona series may or may not take place in the continuity spawned by If and Devil Summoner, although it's heavily implied to be so with the presence of both Tamaki (the female protagonist of If) and Kuzunoha devil summoners in the early Persona games.
It's worth noting that the What If in Shin Megami Tensei if... had the interesting effect of leading to the creation of an Alternate Continuity that has been far more financially successful than the "main" SMT franchise, with eleven games (and that's not including the multitude of Updated Rereleases!) currently released in the If/Devil Summoner/Persona line compared to six in the "main" line, making it one of the rare What Ifs to actually overshadow its parent franchise.
The Devil Summoner prequel games also provide an Alternate History What If, hinging on the Taisho period lasting longer than it did in our world.
Basically, Raidou's antics in the time stream stopped the main Shin Megami Tensei series from ever happening. In fact, most of the MegaTen games brought to America weren't actually released under the Shin Megami Tensei name in Japan, but the localizers wanted to use the main series's title, thus we have Shin Megami Tensei: Persona 3 and whatnot.
Command & Conquer: Red Alert is based on a What If scenario after Einstein uses a Time Machine to erase Hitler from history. Turns out this leads to the Soviets starting the second World War instead. It is also implied to lead up to the first game, which starts out with another What If, a meteorite spreading a strange new material named Tiberium.
Little-known First-Person ShooterIron Storm is set in a 1964 where World War I never ended and is entering its 50th year. In a subsequent re-release (only for the UK market, as far as I know), it was retitled World War Zero.
More recent First-Person ShooterTurning Point: Fall of Liberty features a world where Winston Churchill died in 1931, and the lack of his leadership was the cause of Germans winning WWII... And invading the USA in 1953, when the game starts.
Freedom Fighters by IO Interactive (better known for the Hitman series) put the players in the shoes of a plumber becoming a resistance leader, in an alternate reality where USA are invaded by an USSR that not only never collapsed, but was the real winner of WWII by dropping the first atomic bomb on Berlin.
Real Time Strategy game War Front Turning Point has Hitler assassinated in the early days of WWII and, under his successor, Britain occupied by the Nazi. After the Allies defeat them, the Russian take the chance to invade Western Europe, leading to the merging of the Allies' troops with reinforcements from the recently dismantled Nazi army. All this, with some science-fiction weaponry thrown in.
The Dragon Ball Budokai games have currently always a set of What If stories in Story mode which are usually unlocked when you win a battle that the original storyline has you losing. These range from the serious (Vegeta beats the Z-Warriors when he first shows up on Earth, achieving Super Saiyan in the process) to the silly (Cell accidentally absorbs Krillin and turns into a severely weak, miniature version of himself).
The story mode of Dragonball: Supersonic Warriors gives each playable character an "IF" story, in addition to having a story mode for the canonical events. For example, for Piccolo, Planet Namek is not destroyed and Goku and Piccolo defeat Cell using the same method they used to beat Raditz, and Piccolo revives and merges with Demon King Piccolo to defeat Buu. Also Krillin takes down Cell. Even Goku's IF story is different from canon.
The World Ends With You: Question: What if Tin Pin Slammer was the biggest thing in Shibuya? Answer: TWEWY would be a great Beyblade-parody and Neku a Tyson with "Emo-urges". (As seen in Another Day)
Lord of the Rings: Conquest has a campaign where you fight as the forces of evil, with the question: "What if Frodo failed to destroy the One Ring?" Answer: The world goes to hell.
Mega Man Battle Network could be seen as "What if Dr. Light worked in networking technology instead of robotics?" There was even a part where there is a debate whether to fund Light's (Hikari's in this case) project instead of Dr. Wily's robots.
The Hall of Memories in Adventure Quest is made specifically for this; it allows people to revisit past events and explore what possibilities might occur without impacting the real world.
The Dragon Age: OriginsDLC story "The Darkspawn Chronicles" asks "What would happen if the player's Grey Warden died during the Joining ceremony, and the Wardens were led by Alistair?" Answer: Ferelden is wiped out by the Darkspawn.
Several Gundam video games give the player the opportunity to explore alternate versions of the Universal Century. Gundam Vs. Zeta Gundam's extensive UC Mode offers a few distinct ideas (like "What if Kamille/Amuro/Char joined the Titans?" or "What if Zeon won the One Year War?"), but the most famous is the strategy game Gihren's Greed, which lets the player take any faction from the original series up through Char's Counterattack (and a few original ones like an all-women faction or a scientist faction lead by Amuro's dad) and lead them to victory or defeat. The most recent version even included updated, Zeta Gundam-era versions of several characters who died in the original series like Garma Zabi and Sleggar Law.
Dead Rising 2 "Off The Record" explores what would happen if Frank West was the hero of the game instead of Chuck Greene. Frank became very popular, having ran his popularity in the ground before showing up in Terror Is Reality, wrestling zombies, before the game takes off. Also, Chuck Greene is a psychopath (a non-psychopathic version is Frank's co-op partner), and Stacy is this game's main villain.
Brink has a handful of What-If missions, which follow on from certain story levels if the canonical outcome didn't happen. For example, Security have a What-If mission in which they have to defend a prison to prevent Chen from escaping. The corresponding What-If level follows on from the mission if Security failed to prevent Chen from escaping.
Silent Storm starts as a straightforward World War II game, until the "What If" portion comes into play. What if a powerful secret organization bent on world domination was playing both sides against each other and supplying them with equivalent advanced weaponry in order to cause sufficient damage for the organization to take over after the war? While this would be interesting in itself, the game then had to bring in Energy Weapons and Powered Armor. Hammer & Sickle takes place in the same 'verse but during the Cold War era with both THO and the Sentinels playing their shadow games. If the player (a Soviet spy) fails, World War Three is unavoidable.
The Survival Pack DLC for Left 4 Dead within The Last Stand map explores the idea of what would happen to the survivors if they took a wrong turn and tried to hold out in being rescued. As the tagline says for the poster that shows the whole point of survival mode,It Doesn't End Well.
Fallout asks, "What if the sociopolitical aesthetic of the 1950s had endured for the next hundred years or so?" The results are notpretty, though the progression of the games shows that conditions are slowly improving again... after 120-200 years.
According to the official The Legend of Zelda timeline depicted in the series manualHyrule Historia the split timeline currently hinges on a What If? scenario. After Link is sent back in time by Zelda at the end of Ocarina of Time, he fights Ganondorf, and at that point, one of two things happens. Either Link wins, which leads to the Child Timeline, or Ganondorf wins, which leads to the Downfall Timeline.
From the opposite perspective Ocarina of Time could itself be seen as a What If? to the original games: "What if the imprisoning war of A Link to the Past's back-story could be averted?"
An upcoming DLC for Assassins Creed III titled "The Tyranny of King Washington" does exactly this.
In Fist Of The North Star Kens Rage, this is what the Dream Mode is all about. Every character gets a specific divergence from canon, and you get to play through this imaginary situation.
The PS1Spider Man video game has an entire mode based around this. This changes various elements of the game, such as changing water into lava in the sewer levels and replacing lids of pipes with lids that feature giant bananas.
The DS version of Disgaea Hour Of Darkness includes a hidden "Etna Mode", which gives you an alternate storyline that shows what would've happened if Etna had actually succeeded in killing Laharl at the start of the game, making Etna the protagonist. It manages to be even weirder than the main game.
The video game based on Sword Art Online called Sword Art Online Infinity Moment starts off with a glitch that interrupts Kirito and Heathcliff's Duel to the Death in floor 75 and must go on to floor 76 and beyond. Dragging them along are ALO players, including Leafa/Suguha, Kirito's younger sister.
Resident Evil: Operation Raccoon City, while plays like a generic (and pretty flawed) third person shooter, it is a big "what if" game taking place during Resident Evil 2 and 3. What if Umbrella had a special forces unit sent in to erase the evidence and eventually have to assassinate Leon S Kennedy and choose to follow through with it or oppose their order. What if there is a military special forces unit sent in to investigate the situation and eventually assist Jill Valentine? What if both Umbrella and the U.S. Army enter into skirmishes in attempt for one to erase the evidence and the other to preserve it?
Fire Emblem: Awakening has DLC that pits iconic Fire Emblem characters against each other, with the characters of Awakening getting in the fun. Each DLC pack that features this concept has three variations of it. One where the Awakening cast allies themselves with one faction. Another which pits them with another faction. And a third that has both factions working together against them.
The premise of Evil Dead: Regeneration is that Ash never got sucked into the past (therefore, no Army of Darkness, and by extension, the other Evil Dead games), get's put in a mental institute having been blamed for the murder of the other characters from Evil Dead 2, and fight against a mad scientist hell bent on releasing deadites in the world.
Castlevania Fighter, a fan game with the current plot being what if Adrian (aka Alucard) got killed along with his mother, and Dracula killed Trevor Belmont. The only people able to stop them are others from their old dimensions.
On the NFL's website, there is Dave Damashek's video series, "N-if-L", which shows what happens if the NFL's most memorable/controversial moments didn't happen, whether if it's during the playoffs (e.g., Joe Montana's "The Catch", The Tuck Rule Game) or the Super Bowl (Scott Norwood's "Wide Right" miss in SBXXV, David Tyree's helmet grab in SBXLII).
The Futurama "Anthology of Interest" episodes had the characters view, via one of the Professor's inventions, various "What if" scenarios. In the first one, it reveals that the entire framing sequence is itself such a scenario.
What If Bender Was 500 Feet Tall? He fights a giant Zoidberg and dies.
What If Leela Was More Impulsive? She kills everyone except for Fry, whom she sleeps with.
Parodied when Fry's What If is 'What If Bender Was 500 Feet Tall?', because he liked it and wanted to see it again.
What If Fry Never Fell In The Freezer-Doodle And Came To The Future-Jiggy?*
What if Fry never came to the future?
Reality falls apart.
The second one presents the following scenarios:
What If Bender Were Human? He stuffs himself on food, booze and smoke, and dies of morbid obesity.
What If Life Were More Like A Video Game? Video game characters invade Earth demanding quarters.
What If Leela Found Her True Home? She winds up in Oz and becomes the new Wicked Witch of the West. Unlike the others, though, this was just Leela's dream after she was knocked out and not an actual projection of the What If? machine. Indeed, Leela discovers her true home (Earth) later on.
An episode of Ben 10 springs this on you at the end. Ben finds himself back on the day he finds the Omnitrix. He remembers everything that happened but Max and Gwen don't... and then Gwen gets the watch instead of him. Initially the episode seems to be a time-travel make-things-right-again episode but at the end of the episode Grandpa Max ends up with the Omnitrix and the episode is presented as a What If.. which just makes you wonder why Ben could remember the 'real' timeline.
The Family Guy episode Meet the Quagmires shows what would happen if Peter was married to Molly Ringwald instead of Lois. Al Gore would be president and Chevy Chase would host the Tonight Show.
As soon as Brian finds out that this world is a paradise compared to ours, he insists that Peter leave things be. Of course, Peter can't do that.
The Phineas And Ferb episodes "Phineas And Ferb Get Busted" and "Phineas And Ferb's Quantam Boogaloo" are about what would happen if Candace succeeded in busting her brothers. The results weren't pretty.
This is the entire point of Wild Kratts — what if we had the technology to really get inside the minds of the creatures by effectively transforming into them?