It appears his ceiling is multiple major conference champion and Final 4, based on his actual previous results. His problem was not his ceiling--it was his floor. When things didn't break his way for one reason or another, it was bad. Like "going from ranked #3 to missing the tournament and losing in the first round of the NIT in a game you played on the road because you didn't want to face the home fans after missing the tournament" bad...
It's not magic. It's not that he's missing some thing other coaches are born with. His priorities were violently skewed toward offense, both in coaching and recruiting. He usually didn't teach or recruit defense, and didn't hire anyone to do it for him. The only good defensive teams in his tenure had kids that came in wanting to defend, and understanding that part of the game without having to be coached up. Mainly, it was Zeller, Oladipo, and Sheehey.
People complain about the turnovers all the time...but the turnovers weren't the real problem. The offense was generally good notwithstanding the higher turnovers, because the shots it generated went in more often. But the offense did have a wider range of variability than the average college basketball offense. That's why his ceiling was final four and not national champion. The team was bound, over the course of 6 games in 3 weeks, to throw up a clunker on offense. And with no defense to fall back on, his teams are certain to lose at some point, as the continue to face increasingly stiff competition.
If you can't win a national championship, you won't get to keep coaching at IU. Maybe you can, if you make the tournament every year. Maybe. Crean didn't do that either. Our standards are higher than he could deliver. It's possible, with an adjustment in his priorities, that his ceiling could go up, but I doubt it will happen. He had 4 years after the Syracuse loss to figure it out, and nothing changed.
Georgia might be good for him. They won't demand a tournament appearance every year, and Atlanta produces some talent. That's probably his last job. He'll make the tournament 60% of the time, produce a bunch of highlights and blow-out wins over weak schools, and win a few games now and then. If he can't make it work there, he'll pull an Al McGuire and go into broadcasting.
In terms of coaching careers, this is pretty damn good. Most high school coaches would trade their soul for it. But it's not Elite, of course, which is what coaching at IU requires.