If I were Campbell, I wouldn't have said yes to Nebraska so easily/early. If he's got an agent worth his salt, that agent is telling Matt "just wait until we know what better jobs are open". And look what happened: you have Oklahoma, USC, LSU, Washington, Miami open now, Florida WAS open... if Cristobal bolts, you'll have Oregon open up. Every single one of those is better than the Nebraska job.
It's hard to believe Campbell would have just bolted for Nebraska, knowing all the good jobs that could be opening up. Borderline not believable. The only thing that's plausible about it is if Campbell was dead set on being in the B1G, but realized that all the better B1G jobs are locked up for a while, so why not go to UNL. But the fact that he's going for the Washington job kind of shoots that theory down.