The title is somewhat self explanatory, but basically it could use the values of corpse_decay_time to define this, or have a value of its own so that the body can still disappear after a while.
I don't think an animation would be necessary (who would watch a corpse for days?) but it could change into a skeleton model (or local_texture instead of a model)

This has some merit - with the current code base, I do not know if this is easily doable, but there have been a few attempts (stalled thanks to RL and other projects getting in the way) to clean up and rewrite what is needed thanks to some bugs (such as the "the body doesn't show up for the player" bug that seems to happen randomly)