I'm not sure if I'm reading this right, but are you implying that chins can 'heal' back? There doesn't seem to be a whole lot of scientific consensus about the myth of the chin, so I doubt anyone in this thread can either deny or confirm that. When people generally talk about chins it's just a whole bunch of layman's inference.
What I can say is that every punch that lands is a different scenario. Different velocity/shape/angle/weight, did the fighter see it coming or not, genetics, perhaps things like weight-cutting, etc. Implying Crocop's chin somehow got better again because he started racking up wins after his UFC stint, is circumstantial evidence at best, and that's still kinda stretching it. Might simply be a case of the right punch not landing on him post-UFC.
I also think people tend to overrate the idea of having a 'good or bad' chin, imo it's much more a defensive issue, than a genetic one. Nobody is supposed to take trauma to their brains, anyone will eventually get hurt by a punch. Arlovski got put put out cold by Fedor because he took a calculated risk (which exploded in his face) by running face first into the overhand of a very explosive, very dangerous mofo. Against both Sergei and Rogers he backed up in a straight line with his back against the fence. Those are all much more examples of bad fight IQ, nobody should rely on the perceived strength of their chin against heavy hitters like that.
Same goes for fighters like Pat Barry, makes for super exciting fights though!