Main concern if CMC leaving would be that the success hasn't been sustained long enough for me to think the next person is going to be as good.
Also the 'stepping stone' narrative would be back.
The stepping stone narrative will always be here to an extent. Campbell changed the conversation from "you can't win here" to "there are great things about the job, but it's not easy to win here." There are enough disadvantages outside of the coach's control, and outside of what Campbell can likely do that it's never going to be considered a top tier job. Still, having a passionate fanbase that continues to grow and take market share from it's local competition and a highly supportive AD go a long way to attracting a good coach.
If I had to bet on one scenario, I'd bet on Campbell being at ISU for 4-5 more years, then getting an NFL job that at least has demonstrated competent ownership.