Well, if we're talking about Boeheim, then it's either NBA or retirement. I'd never forgive him for going to another school (not that he ever would).
But if I was a Butler fan, it'd probably be just as easy for me to accept a guy like Stevens going to the NBA as it would be if he got, say, the Duke gig. It really depends on where your team is on the food chain.
For example, I'd have been pissed if I was a Kansas fan and Roy Boy jumped to UNC since that was basically a horizontal move, UNC ties aside.