About the only job that would tempt him away is the Ohio State HC position...and that looks to be in solid and stable hands. Mid levels like Tennesse or even Florida State aren't really a threat...as, believe it or not...Iowa State will match any thing they can pay right down to the assistant level. But more importantly, Campbell likely DOES want the OSU job...or at least something comparable (in the Midwest, where he is comfortable) like a Penn State, Oklahoma or perhaps even Texas. Anything less, and he will simply stay and keep building what he's started, an act which will only serve to raise his stock when the opening he wants at an elite midwestern school comes open.
By all accounts, he and his family LOVE the Ames area...unlike guys like Chizik who reportedly despised it...and he sees himself as a builder, a man who wants to leave a true legacy. So while I would agree that he will in time move on to something bigger, its not going to be this year or even next season...perhaps after 4-5 years of sustained success he will be lured...less by money...than by the challenge of running an elite program like Ohio State.