The Disney Villain Death is so ubiquitous, so frequent that any five year-old knows what you're talking about: The part where the bad guy drops into a bottomless pit and dies.
You can probably name a million instances on your own. There's the Evil Queen in Snow White and the Seven Dwarfs, Ratigan in The Great Mouse Detective and memorably the Hunchback of Notre Dame. Each movie usually adds their own twist to the formula, like Frollo slipping off the top of a cathedral while holding the phallic symbol of his sinful lust before landing in a sea of molten copper.
The trope goes far beyond the bona-fide classics. This thing is everywhere, and hasn't shown any sign of stopping. Even Pixar isn't safe, as we saw in Up.
The plague extends to direct-to-video refuse like The Lion King 2, where the low budget paralyzed Zira's animation while she plunged into a raging river.
In the Rescuers Down Under, McLeach escapes crocodiles only to fall down a waterfall.
Ever the company men, Mickey, Goofy and Donald have gotten in on the action. Together they chopped up the famous beanstalk, which caused a giant to tumble down to his doom.
More recently, Tangled villain Mother Gothel had the misfortune of rapidly aging and then dropping down the side of a 70-foot tall tower.
Treasure Planet is a special case; the mutinous Scroop accidentally escapes the ship's gravity and falls up into the infinite vacuum of space.
Pitching bad guys off a cliff is probably the most practical way to go about getting rid of them. We watch them descend into the void and vanish, but rarely do we ever see the moment of their death. Their demise is implied, and we don't have to think about the grisly details as long as we don't see it. Out of sight, out of mind, right?
But imagine what those fleeting, unseen moments must be like for the doomed. There's only a few seconds of weightless flailing before they end, but the sheer terror must stretch it out to an excruciating degree. Hell, think about what it must have been like for that warlock from the DuckTales movie; he fell from his fortress in low orbit down to earth. Dude's got about five minutes of contemplating his mortality and recounting every regret in his life.
We get to forget about these characters the moment the camera cuts away, but they still exist out there, somewhere. For all we know, the fall didn't kill Gaston; maybe he was paralyzed on those jagged rocks, and remained helpless for hours before finally succumbing to internal bleeding.
It's doubtful that anyone found Gaston's body. It's probably still down there somewhere, rotting below Beast's castle. Disney is responsible for the things that they choose to animate, but they should also consider the implications of the things that they don't animate.