I'd be surprised if Campbell actually went to Michigan - it's really starting to feel like he truly wants to be here long-ish term - though they'd be smart to pursue him.
But if/when Campbell leaves, Michigan is the type of job I could see him leaving for. Among the blueblood program jobs it's relatively low-drama, relatively sane fans, good fan support in numbers if not quite as much passion. (Lots of "relatively-s" here because it's college sports...there's always drama and insane fans.)
Compare that to other blueblood jobs like Texas or USC or Florida State where there just doesn't seem to be a cultural fit.