O'Brien had a good year, better than he had any right to have, but some of it was just by default because Paterno had let a lot of things get really bad from a pure football standpoint. So, he didn't perform a miracle. That said, he's done a hell of a job recruiting with limited scholarships available and seems to get all of the players to buy into his system and his message.
If he leaves, we lose the 2013 recruiting class, a class that is holding the potential for the program to survive these sanctions in its grasp. It has a top quarterback, a top tight end and some very good B-level type recruits who can make an impact. Losing that class kills the program.
More importantly, it will totally break the spirit of the fanbase. Which I guess is the point of the sanctions, so people like Headache will probably be thrilled if he leaves.