Snow White and the Seven Dwarfs (1937): While the dwarfs are washing up, Dopey accidentally swallows a bar of soap. This was originally resolved in the very next scene, but that scene was cut during production.
If you pay close attention to the Queen's scenes after learning of the Huntsman's failure to kill Snow White, you'll notice that she doesn't interact with the Huntsman once before she dies, which means the Huntsman lives to see the end of the film. And in case that doesn't make it clear enough, the Screen-to-Stage Adaptation at Radio City Music Hall in 1979 had an original scene where he and the Prince reported to the King that Snow White was still alive. He's extremely lucky that the Queen decided to get rid of Snow White straight away instead of punishing him first. That does happen in the Perspective Flip novel Fairest of Them All — she stabs him with a knife (and the red blood gives her the idea to use a poisoned apple on Snow White) — but it's unclear whether he dies of this wound or not, so that would qualify as a straight example of this trope.
While Princess Yum Yum is bathing, the Thief steals her back scratcher. In the American version nothing comes of it. In the original version, the Thief steals two back scratchers and uses them to escape having his hands cut off.
While Tack and Yum Yum are consulting the Witch, the Thief is trying to get a giant ruby on a tower by flying with palm frond wings. He ends up crashing into the Witch. But since the American version eliminates nearly all the footage of the Witch, the Thief's fate is left literally up in the air.
The American Version cuts out the Mighty One-Eye's death and even has him still alive when his machine collapses, because in the background you can hear him say "MY MACHINE!" But Tack later says "King One Eye was defeated for all eternity", which could only happen if he was dead... I guess we'll assume he was on top of his machine as it burned, and was trapped with no way out and burned to death.
There is also a literal example: Early in the film, Tack is seen feeding a mouse while he's imprisoned, and we later see that he's sneaked the mouse out with him when he escaped (these shots are present in all versions of the film). While it's never seen again in the edits, in the original cut he removes the mouse from his pocket and gives it to YumYum before he goes to face One-Eye's army.
In Corpse Bride (2005), Victor's parents are last seen on an out-of-control carriage whose driver has just died. They don't show up again.
Although they must have lived, as their death would have been revealed to Victor in the same way as the driver's.
Lilo & Stitch (2002) begins with Lilo feeding Pudge, a fish she claims controls the weather. He's never mentioned again, outside of two deleted scenes: one where he's killed by seagulls, and Stitch accidentally kills him. He does make a proper reappearance in the TV series, though.
Plus, you can see Pudge swimming by with a sandwich in Lilo's first scene.
In The Rescuers Down Under (1990), Wilbur's mouse plot is resolved before the credits, but no second thought is given to saving everybody back at McLeach's hideout.
Not to mention, one of the main plot points was rescuing the golden eagle so she could return to her nest. The film ends with the hapless seagull, who was left egg-sitting, panicking as the eggs begin to hatch. So much for the joyful reunion viewers were expecting...
Likewise in Pinocchio (1940) no second thought is apparently given to save the boys on Pleasure Island or asking the fairy to restore their humanity.
Mirage is last seen helping the Parrs reach the OmniDroid in time to stop it before disappearing for the rest of the story.
In the comic series, Mirage appears to have avoided severe punishment for her role in Syndrome's plans and now works as one of Rick Dicker's NSA agents. She and a reluctant Elastigirl agree to work together to investigate the disappearance of the Eiffel Tower in relation to Xerek.
When the supers are forced into retirement, the existing villains seem to disappear as well, and it's never explained what happened to them. It may be that the government did keep some of the supers fighting the good fight without the flashy codenames and costumes... just not the easily recognizable headliners like Mr. Incredible, of course. Or the military could take over. There was at least one fan fiction that explored that mouse, suggesting that at least some of the old villains joined the private sector.
Maybe the government has been purchasing weapons to help them deal with villains from Syndrome?
Probably got boring when trying to take over the world when there isn't someone trying to stop you.
In Titanic: The Animated Movie (2001), the ending shows virtually everyone who is named and given a backstory (or as much of a backstory as the characters get) escaping onto lifeboats, except for Molly (the singer), Winnie (the gold digger), and Jeremy McFlannel (the banker). It's later established that Molly drowned while singing with the orchestra as the ship sank (no explanation for that), but nothing is said about Winnie or McFlannel's fates. This is pretty strange, when you consider that the movie goes out of its way to hook all of the characters up in the epilogue, regardless of whether or not they'd met before. The writers may have been going for a kid-friendly way to kill the evil banker that didn't die in the original James Cameron movie.
The uncut version heavily implies that they died together on the ship. The last they're seen, Winnie refuses to get on the lifeboats and insists on staying with McFlannel, even though he asks her not to "sacrifice [herself] for [him]".
At the end of Shrek 2 (2004), after part of the credits, we see Donkey's children. He had six, one red Dronkey. She never appears in the third movie. She was the most popular for merchandise too.
Early on in WALL•E (2008), we learn that the Axiom was only one of a large number of ships used to evacuate the Earth. "BnL Starliners leaving each day!" But we never find out what happened to the other ships, or the (presumably) huge number of people that lived on them.
Considering the technological advancement of the Axiom itself — it makes its return trip literally in seconds — it is not outlandish to assume that when the Axiom processed its return, that it also sent out similar signals to the other ships.
Or, on a more sinister note, the other ships are all still cruising the Kuiper Belt, as their AUT Os believe they have no reason to return to Earth.
The Tale of Despereaux (2008). What the hell happened to the weird guy made out of fruits and vegetables after Despereaux left him to rescue the princess? Did the rats eat him? Was he just left there to rot? Or was he just a part of the chef and mouses' collective imagination?
In the animated adaptation of Charlotte's Web (1973), Wilbur's best friend besides Charlotte is a gosling named Jeffrey who wants to be a pig when he grows up, he is last seen trying to join Wilbur, Charlotte, and Templeton in the crate but he is spotted and Avery pulls him out, after Charlotte dies and Wilbur returns to the farm Jeffrey is nowhere to be seen.
In Disney's The Princess and the Frog (2009), Charlotte's dog, Stella, is heard to speak when she recognizes Tiana just as Naveen and Tiana float away. Although other animals talk throughout the film, the dog is never seen directly interacting with Tiana while she's a frog besides that one line.
Apparently, Stella was originally going to part of a sub-plot, but it was dropped as the directors thought that there'd be too many talking animals in the film.
We never find out what happened to the cat Charlotte had in the opening scene either, but a lot of time went by in the interim, so there's an obvious explanation in that case.
In Duck And Cover, the monkey with the firecracker seems to be a suicide bomber, since he's nowhere to be seen after the explosion and the tree is destroyed. Either he jumped away at the last minute or there are several monkeys.
In the obscure German animated film The Magic Voyage (1992), throughout the movie a trio of rats become Pico's unwilling companions aboard Columbus' ship. Near the end they crash onto an island while the rats decide to escape by manning a lifeboat; during the crash they collide with the boat causing it to wash up on an island. When the rats are recovered from the wreckage the leader is nowhere to be seen and remains missing for the rest of the film; it can be assumed that he died in the wreck and his absence goes unmentioned by the rest of the characters.
The Evil Chancellor never becomes important to the story and just disappears after Columbus's meeting with the King.
In The Prince of Egypt (1998), the two comic relief villains (turned menacing in their song), Hotep and Huy, are last seen during the plagues, with boils much like the others Egyptians, and Rameses overturns a table and sends them away. They are never seen following this. Possibly they were burned by the flaming hail, or maybe Rameses was firing or banishing them, or they were both first-born sons.
Most likely they were fired, because if you listen closely, you can hear Rameses yelling: "Get out!"
In the Spiritual SequelJoseph: The King of Dreams, there's the fate of the imprisoned butler and Zuleika. The butler was presumably pardoned as Joseph predicted, but there's no explanation as to why Joseph remained imprisoned for so many years after asking the freed butler to clear his name (the Bible says that the butler forgot, but it's never mentioned in the movie). The last anyone sees of Zuleika, she has Joseph imprisoned for refusing her advances. She never shows up again, even after Joseph becomes her husband's friend and marries her niece.
The butler is at least seen serving Pharoah Joseph.
Turaga Dume in BIONICLE 2: Legends of Metru Nui was found comatose inside a pod by the Toa. They said they would return to rescue him later. He is never seen or heard of after that, even when all the Matoran trapped inside their pods have been freed. They planned to tell his tale in an exclusive story, but later claimed that his pod simply malfunctioned when we weren't looking, and he got free.
It would've been solved if they hadn't skipped the last three parts (and the trip from Metru Nui to Mata Nui with all the Matoran pods) of the story in between the Glatorian saga and the Visorak saga, right before the six matoran of Mata Nui (The Island) left for Voya Nui that Turaga Dume stayed in Metru Nui to prepare it for the eventual return of the Matoran.
In the 4th movie, The Legend Reborn, Tuma vanishes after being defeated by Mata Nui. While the movie does make it look like he died there, he was only just knocked out and was set to appear in the scrapped sequel. Strakk has a bit of this as well, as we last see him walking out of the arena after his defeat — originally, he was to be banished to the desert for breaking the rules of arena combat, but this issue isn't brought up in the movie, so it's unclear whether or not he walks away unpunished, which, given his negative portrayal in the film, seems weird, as it makes him a loose villain.
During Mushu's introductory scene from Mulan (1998), he is tasked with awakening the Great Stone Dragon from its statue form, and ends up destroying it instead by hitting it too hard with his gong. This is not brought up again.
Toward the end of The Jungle Book (1967), Bagheera can be seen persuading several elephants to help him and Baloo find Mowgli before Shere Khan does. The elephants then all march off with Bagheera, but even though Bagheera comes back after Mowgli defeats Khan with the help of Baloo and some vultures, the elephants do not.
Those three bimbettes from Beauty and the Beast (1991). They constantly accompany Gaston during the first half of the film, but for some reason are completely absent during the last half of the film where the villagers are raiding the Beast's castle.
The musical adaptation has them included among the villagers who go to attack the castle. Presumably they are scared away along with everyone else, in the ensuing fight.
In Disney's Robin Hood (1973), both Maid Marian and Lady Cluck are active participants in the riot following the archery contest and the following The Villain Sucks Song, for which Prince John has the whole town thrown in jail. However, Marian and Cluck are not among the prisoners, nor are they seen during the Jailbreak scene which ends with the castle (her residence) being set on fire.
They do however return at the end of the film when Robin Hood and Maid Marian wed.
The original ending would have given Marian more of a role in the ending. Prince John would have stabbed Robin Hood and chased him into a church, where Marian also was hiding. While Robin Hood is lying on the ground, Prince John proceeds to threaten Marian, until King Richard shows up to save the day. It's possible that when that ending was cut, there wasn't a chance to give her a proper appearance until the wedding.
Throughout the entire film, the villainous owl from Rock-A-Doodle (1991) is constantly accompanied by six henchowls (not counting Hunch, his nephew). But at the end of the film, there are now only five henchowls left (still not counting Hunch)!
In Finding Nemo (2003), after Nemo manages to escape into the sewers, it pans up ominously to show that he's headed into a sewage treatment plant. The plant never actually comes up again in any capacity, and the next we see of Nemo, he pops out of a pipe and ends up safely back in the ocean.
The script originally contained a scene explaining how Nemo survived his trip through the plant, but it was cut. The ominous shot of the plant was probably a set-up for the (apparently rather harrowing) deleted scene.
Nigel the pelican is last seen sadly returning Marlin and Dory to the ocean, all three believing that Nemo has perished. He gives his condolences and flies away, never learning (on-screen) that Nemo was actually alive and well.
Although the first few lyrics of the song "Hakuna Matata" from The Lion King (1994) focused entirely on Pumbaa's backstory, it for some reason, did not mention anything about Timon's backstory at all. However, Timon's backstory was finally resolved in the Direct-to-Video sequel film The Lion King 1˝ (2004).
His backstory was mentioned in a deleted scene, not unlike the Lilo and Stitch example.
The official comic book adaptation has Timon explain his backstory during the Hakuna Matata scene, while Pumbaa's goes ignored.
Better examples are Sarabi's disappearance in Simba's Pride (1998). You could argue that she wasn't really popular enough or her voice actress died and a replacement wouldn't sound suitable. As well as in Simba's Pride near the middle of the film as Simba teaches Kiara a lesson, a baby African Pygmy Kingfisher is seen trying to fly from its nest only to be stopped by its mother. It disappears without explanation.
In Ali Baba & The Gold Raiders (2002), Ali Baba's brother disappears from the story once the Gold Raiders come back and find him in their cave. It should be pointed out that in the original story the Forty Thieves killed him, so it seems the writers just couldn't be bothered to think of a way to write him back in aside from Ali Baba returning with a large sack he didn't have when he left, hinting at his collecting his brother's remains.
Cars 2 (2011) is apparently about Lightning McQueen competing in a race taking place in different cities around the world while his friend Mater is recruited as a spy so that he can help British agent Finn McMissile fight an evil organization of villainous, beaten-up cars. However, during the last third of the film, which takes place in London, England, the race McQueen is participating in is mysteriously interrupted by the conflict between Mater and McMissile and the Lemons, and as a result the race in particular is never brought up again after that.
It's implied that the big race in Radiator Springs is the 'replacement' final round of the Grand Prix.
Sylvia from the Direct-to-VHS movie An Extremely Goofy Movie (2000). She doesn't pop up outside of that film or is mentioned - even Roxanne from the first movie popped up in House of Mouse. It may be Justified by the Goof Troop continuity being all but done, and the movie only takes place in that continuity.
Happy Feet 2 (2011): The last time we see Sven is when it's revealed he is a puffin, not a penguin, and is a complete joke, what happens to him afterwards other than helping dance the iceberg to bits is not explained.
In An American Tail (1986), the young baby of the Mousekewitz family, Yasha, drops out of the film about halfway through. She does appear in the sequels, however.
The first half of The Simpsons Movie(2007) focuses on Homer getting a pig, Plopper. But halfway through, the pig disappears and never returns in the second half (though he briefly appears in one of the alternate ending sequences on the DVD).
A Charlie Brown Thanksgiving opens with the classic "Lucy & The Football" gag. However, after this opening scene, Lucy is never seen again in the entire special!
Earlier on in the film, Bill the Lizard is blasted out of the White Rabbit's chimney and up into the sky while trying to extract the giant Alice from the Rabbit's house. He isn't seen again for the rest of the film.