for the chance to get promoted when his boss flames out is a sketchy basket to put all one's eggs in. Who knows how long it will take Sitake to move on. It's not like he's old and planning to retire soon. Unless he's comfortable being a DC for a while, he'd have to consider it.
I don't think it would hurt BYU much in the medium term, he'd jump at the chance to come back to BYU if/when Sitake leaves. But maybe USU realizes that and would want to look elsewhere.