He didn't want to be the "Man Who Replaced The Man", ie, Ron Zook. I'm hoping that he'll stay about 2-3 more years while Will Muschamp implodes the program, then he'll go to Florida to pick up the pieces.
It's certainly good to have such a nice fan base like tMSU. Even if he leaves after a few years, he'll remember his stop here as the happiest time of his life. Being a good place to work is worth at least a little bit of change.
That said, Dan Mullen is looking like he's set to become a big-time coach and we're lucky to have him for as long as we can.