That issue likely won't be resolved when the phone starts ringing if Harbaugh doesn't put up a monster year this year. And with that in the air (or resolved with a resounding "Sorry Clowns, yer out") Campbell is not going to turn down Michigan if they call. No way. They will be able to offer way more money.
Look, I hate Michigan, but there is something magical about the Big House. You cannot fly out of Ames at 7 AM and go for a tour of Ann Arbor that same afternoon and not be tempted. And then the money. Michigan will offer a blank check. The guy will get an offer probably around $8 million. There is some combination of loyalty, facilities improvements and money that can sway a guy like Fitz to stay away from Michigan, but if you're not an alum of the school you coach and sitting on a really long history, the statements about "loyalty" from 5 or 6 years ago mean F all.
Michigan might be the best job in all of college football. They're not gonna give you forever, but you aren't gonna get thrown on your ass if you have a losing record the first two years (which Campbell wouldn't). And even if you get run, it's a high enough tier job that you're still totally marketable for another P5 (P4) level job if you want one (RichRod). It's a job that takes a helluva combination of factors for someone to turn down.