I think there are 2 issues there:
1. Fan support: Including myself, I think a lot of fans will simply just check out if Frost fails. Still tune in on Saturdays, sure, but just won't be as big of a deal to people anymore. Like Mike Riley level excitement.
2. very slim chance you get Matt Campbell. He's an Ohio guy apparently. So, without him you're looking at hiring another hot G5 coach trying to work their way up? Great, just did that with Frost. Reality is if Frost fails, Nebraska becomes a Power 5 stepping stone program on the way to an elite school after an 8-4/9-3 season.