If Harbaugh goes to Michigan, I think he'll be gone in less then five years.
It is a ego thing. He has unfinished business in pro ball. Not to mention his brother has a SB ring.
If you need an example, just look at Dennis Erickson when he left OSU for the Niners. He had didn't like the way things ended in Seattle and wanted to finish things on his terms.
I wouldn't be surprised if Mora bails for the NFL from UCLA in the near future as well.

I personally think Harbaugh should go to the Raiders. At least he'll have something there he never had in Santa Clara. A real QB.......
SF