Well, since Ristul is corruption itself, I wouldn't say so. As long as there's enough corruption, he can do his thing. And AFAIR it was hinted, that he's not an entity like most horrors, but something akin to a semi-sentient force of 'un-nature'.
Anyway, arguing over the top Horrors is kinda pointless, since they're waaay out of any league worth playing.