When I refer to an established, good coach I would say any of the big boys in P5 that aren't on the hot seat and are making good bank. If they're not in the hot seat, they're probably winning consistently enough to keep their fan bases happy, and if they're in the Top 15-30 in salary then they're not going to come to ND to make the same cash or less. So, that's why I say the next coach is going to be a relative unknown with recent success, likely someone at a Group of 5 program in the midst of a Cinderella run or a smaller P5 program enjoying similar success.
I'm not sure I get the Harbaugh connection. I'm not saying it doesn't exist, I'm genuinely curious. To my knowledge he has no academic ties to ND, and he doesn't have any employment history either. How does his family situation come into play, especially if we don't play Michigan for another 14 years? [EDIT] Daughter at ND, I forgot. Maybe that's enough, who can say though.
I'll say this much for Matt Campbell: he's taken 3 star talent at ISU and done some great things. They haven't hit double digit wins or anything, but they've been competitive in every loss since his first season. No blowouts the last few years, and they've been competitive with all the big boys in the Big 12. That said, he's one of the favorites for the FSU job, I would expect he lands there instead.
As far as coaches flaming out and ended up at crummy jobs, that's kind of expected, right? The point I was going for is it's obviously harder to win at ND than it is an tOSU, Florida, or most other big programs. If you have the option to go to a football factory or ND, most coaches take the traditional football factory because there's a better chance you succeed. It's a better career move. When the margin for error at ND is smaller, it's just too risky when most good coaches have a path of less resistance available.
There was one coach that got fired and still found himself in promising positions at a few different stops: Kiffin. Going from the Raiders to UT was pretty decent, it was still considered a good job at that time. He left on his own accord to go to USC, and then after being fired he wound up as Saban's OC which is almost a lateral move these days when you consider Saban's lackeys all get HC jobs of their own after a year or two on his staff. The move to FAU is a bit head scratching, but I'm sure he thought he could use his newfound knowledge to parlay that into a better gig once again. For what it's worth, he's also expressed interest in the FSU job.