While I think we're a few years away from having to worry about this, I remember as a 16 year old being crushed when Doug Dickey left UT to return to his alma mater, Florida. He had it all in Knoxville including having relegated Bear Bryant to also-ran status and a loaded roster that was ready to compete for National Championships. I mean LOADED, especially on the defensive side of the ball. We were Linebacker U, All American after All American including Hacksaw Reynolds, Steve Kiner and Jackie Walker at the same time. The offense had Bobby Scott at QB and eventual Blue Angel, Curt Watson at RB.
But the call to his alma mater was too great and he left to go home where he failed. I've never forgiven him.
Then, of course AD Bob Woodruff, another Florida grad, who was terrified that Johnny Majors would eventually push him aside, passed over Johnny for head coach ( Majors was building a winning program at then moribund Iowa State and was begging to come home) and hired 30 year old defensive line coach, and Alabama grad, Bill Battle as head coach. Battle proceeded to destroy the Tennessee program. Majors then goes to Pittsburgh, that went 1-9 the season before his arrival, and within 6 years was National Champions (was at that Sugar Bowl since my best friend in flight training in Pensacola was a Pitt grad).
Majors then leaves Pitt to return to Knoxville. Trust me when I say Pitt fans couldn't believe he left them.
Bottom line is you never know what someone is going to do when it comes to coaching the college they graduated from.