I think the limit of Ukrainian “cooperation” would be refraining from attacking Wagner forces as they either fight Russian military within Ukraine or withdraw from Ukrainian territory. With the condition that if Wagner isn’t doing one of those two things then they’re back on the menu.

It’d be nice to capture everyone, investigate them all to find the ones who’ve done warcrimes, and prosecute them in an orderly manner. But if plan B is “they retreat from Ukrainian territory in chaos and go fight Russians on Russian territory” I think it’d be great to let them do that. Fewer Ukrainian deaths going forward from that.