It's more than likely that they've fallen from a ledge or a tower a long way to an assumed demise out of eyeshot.
The technique of depicting a death without violence became so popular in the studio that it eventually became a noted trope on TV Tropes.
Think Gaston, Scar, Frollo, Maleficent, Captain Hook, the Queen from Snow White - even the Carnotaurus in Dinosaur.
Take a look at how many in this supercut follow the rule:
There are some exceptions obviously, such as Shan Yu's death via firework in Mulan - itself a move by the studio to avoid a 'falling from a great height' death.
The reasons behind the popularity of the stock demise are pretty simple.
Dying in this way obscures gore and violence from impressionable young minds and keeps the films family friendly, and if they slip and fall, or a ledge breaks, it means the hero of the story hasn't explicitly killed them.
Meaning you can be supportive of the triumphant hero as a non-murderer.