Being dominated by Bama in the playoffs last year with his best team ever had to put a realization in that he isn't winning a title at MSU. Not to mention it was by a coach that bolted MSU because he realized he couldn't win a title there.
Now he is in a down year which is probably solidifying that thought. If he wants a chance at a title, he needs to make a move. And he isn't getting any younger.
If ND wants him, present themselves well, and pay him then I personally think he'd bite.