I think this is about the only way he would leave any time soon. And it could happen. If it does, I'm OK with it.
Unless something changes, I have a hard time he'd leave before the end of next season just because of the way he's set up for a big year.
After that, you'd think he'd be able to get an NFL job if he wanted it. Not sure he'd want to make that jump though while his kids are in school. He would no longer have recruiting to worry about, so the off season would be better, but he basically wouldn't get to see his kids at all during the season, and his off season would be shorter.
As far as colleges go, I think Mullen was ready to listen to offers a few years ago. I don't have any inside info, but I suspect the list of colleges he would consider has shrunk considerably, both because there are so few that would pay him any more, and so few that would give him a significantly better chance to win.