>>47259551More people die of course.
>>47257378Not slavery.
Happiness stat exists in the game. Even if my ghost Pokémon are dead people, so long as they're at high happiness, I effectively have confirmation they're battling for me because that's what they *want* to do with their afterlife.
Also, when Pokémon that aren't my permanent party members have shown me every form they have, I'm done with them for dex purposes, so I release them. It's for the very reason you describe: I don't want to think about putting them in limbo.
