Maynards chops certainly survived their share of abuse. But there was even harsher activity going on on the inside. MF played with a "dry embouchure", meaning that just before he would play he wouldn't lick his lips, he would dry them on the cuff of his shirt. This would give him a good "grip' on the mouthpiece. The combination of that and how his lips pressed on his teeth resulted in him building a callous on the inside of his upper lip.
The callous had its own life cycle: There would be a point in the growth of the callous when it would allow MF to play pretty hard all night, but the callous would still be small enough that he could still play with some flixibility and subtlety. As the callous grew, MF would gain endurance, and could really scream all night, but would start to lose the flexibility. THEN, there would be a night when he would be pounding away, and the callous would crack. MF would go back to the hotel after the gig and take a long hot shower, steaming and soaking the callous, then he would...uh...remove the callous!
He might mention it on the bus the next day, and that night his power and endurance would be a little down, but he would have tremendous flexibility and suppleness.. And the cycle would begin again...
Nasty Buisiness!