It's usually called rehab.
Name one band/singer that has been as good or better after they cleaned up.
And I don't mean commercially better.
I can't say that for Greg Allman, his days with Duane and Oakley were the best of that band. They have had flashes of brilliance with Trucks and Betts but not like they used to.
If there is one I would have to go with Zakk Wylde. His guitar playing is as good as it was with Pride-N-Glory and early BLS. That is when he finally came into his own, I think he has gotten better with his last two albums. They are great. Both released since he sobered up.
Overlord - Black Label Society.
EDIT: In saying that, yes, most bands are not as good when they get off the hookers, blow, smack and booze.