I don't worry about the Michigan job as much as I do the Raiders. Harbaugh, from the stories I've read, is close with Al Davis, has aspirations to coach in the NFL, several of his current assistant coaches at USD have Raider ties and experience, and since Davis changes coaches once every three years or less, that is the biggest threat. (Similar to Jerry Krause's relationship with Tim Floyd).
With that being said, he would still have to have success at ISU within the next three years to justify Davis (if he is still alive at that point) hiring him, and that success would have to be a minimum of a B12 Title. If he does that, similar to Floyd, I don't care how long he is here, I just plan on enjoying the ride and know that JP would do another good job hiring if that situation were to occur.