He's a great defensive coach and with the right people he could have done well. The front office undercut him left and right, they didn't replace the players they lost with anyone good and he was trying to coach Parcells' guys. There is a huge difference with coaching in the NFL and the college game as at the pro level, you are at the mercy of your stars and bad contract decisions made by the front office. In college you can screw with a guy's future earning capability. In the pros it becomes a lot harder.
Ty Law was interviewed for a story about Pete Carroll and he said that if you can't play for Pete then it's really your problem.
If I were him I'd stay at USC and become an all time great college coach.