Strut certainly, because he is badly influenced by Ozzy, if Ozzy one day pushes him over the edge, and Strut turns on him, I can imagine, that without Ozzy, he won't be villain any more, and could even befriend the gang.
Then maybe Thud, but if he meets the gang again at a later time, and would be with Screech and Red Claw again, I really cannot anticipate, what would have happened.
Other villains do not seem to regret anything, because Rhett, Pterano, Hyp, Mutt, Nod, are not full-fledged villains, and others, like Dil, Ichy and Rinkus really do not seem to reform themselves out of the blue, let alone Sierra and Ozzy, who are even full-fledged psychopaths.