As much as I don't like RichRod, I think it was a dumb move to fire him unless you knew for sure you could get Harbaugh, Patterson, Petersen etc. Unless you already had something in place with one of those guys, you are better off just trying to fix the defense and keeping RichRod. Offense wasn't the problem; it makes no sense to start all over again and bring in a new system and set yourself back a few years again unless you are 10000% positive you will succeed with a proven guy.
You put Kirby Smart or Bud Foster at DC for that Michigan team the past 3 years and they would have been easily competing for Big 10 titles by now. They should have just tried to find a good DC.