Final Fantasy VI Randomizer

I would simply redirect Possess's routine to utilize the normal Death routine, except bypassing most immunity and probably hardcoded to not affect any boss creature (index 256+, narshe guard captain, magitek-armor, holy dragon) and make it remove the character in the same manner as Pep Up.

There would also need to be a check at the end of battle to ensure one person is present and alive, and to trip the game over routine if not, in case, say, Terra were to spawn with it at the beginning of the game.