I feel like a complete tool for asking a question like this but could BYU bring a breach of contract suit against Nevada? Obviously they can't force Nevada to honor the contract but they could ask for compensation for revenue lost by having to schedule a I-AA team. Duke backed out of a game with Louisville and U of L filed a breach of contract suit against them:
"The suit claims U of L was unable to find a team of 'similar stature' to Duke and is now short an out of conference game for next season and 'was forced' to replace Duke with Indiana State, which is not a member of the Football Bowl Division, for 2009."
http://www.courier-journal.com/apps/pbcs.dll/article?AID=/20071108/NEWS01/71108013
Anyways, just a thought. I know Northern Iowa is a really good I-AA team, but I still think playing them is going to hurt BYU's SOS and season ticket sales.