Lots of reasons to leave...I assume taking a head coaching gig at Indiana likely means $3 million. Not a year, but perhaps a 4 year contract for at least that total. Assuming he doesn't break any NCAA rules, that means $3 million minimum even if he gets fired in year 2 or 3. It'd take O'Keefe what, almost 10 years, to make that as OC, assuming Ferentz sticks around that long.
Also, maybe he's tired of the vanilla offense he's forced to run and wants to go back to being a head coach with an innovative system.
And for all the Hawk fans chirping about helping him pack, how would you feel if he took two or three assistants with him? What if Eric Campbell went as offensive coordinator and assistant HC, and Rich Kaczenski left to be O'Keefe's defensive coordinator?
If O'Keefe leaves, it's likely he won't be the only one.