Ah, now wouldn't it be funny if Dark Carnival as a guild were disbanded for accepting the convicted non-omni back into the guild?

Yeah, he avoided the 'sentence' and is now Omni again.

Likely there's no code to 'force' you to remain neutral in the game, they didn't think of that one. Probably have to create a whole new 'faction' that's 'criminal' or somesuch, that can't use the side-change stuff.