Fred came to ISU to try and build a winner to see if he could parlay that to get a shortcut shot at an NBA coaching gig.
If he'd have failed from the beginning, he'd have been ok with it, and probably could have gone back to the T-wolves and been fine. Once he succeeded however, he either had to maintain it (difficult given the recruiting needs of that style of play) or get out of town to a different job in college or the NBA. Because the only other option was to fail to meet his own standard he had set and be the golden boy who got himself fired after a (probably too long) decline. Imagine the **** show that would have been for JP! I'm sure they discussed that before Hoiberg ever took the job.
That was never going to happen. Once he proved himself Fred was ALWAYS leaving for the first credible opportunity, his brand as an ISU legend fully intact. Fred got exactly what he needed from coaching ISU, and ISU did too. It was a ton of fun but when it was over, it was OVER. The calculus is different now. A return to the sidelines as Cyclone coach will never happen and most people understand this.