Now I shall be Dr. Phil Taking on another head coaching role at the age of 66 is probably just about remaining busy and having something to consistently do at this point. For the next 4-5 seasons, I'm sure he feels as if he'll have enough energy & life within him to do an adequate job in his mind. I believe he should walk away from the game all together. Simply speaking, from what I've read, he's just not ready to retire. It seemingly appears he's ready to commit to another multi-year contract.
Or it could be another thing on the opposite side of the spectrum. That being what I've always heard of how he's always been on a total power trip. I've read several articles describing his iron fist nature while stating how he's got an unquenchable thirst/hunger for absolute unquestioned control. Upon his firing from UK, a Wildcat insider wrote a piece where he truly referred to the way Tubby used 'brainwashing', and countless fear tactics, among other unfavored methods. Lastly the writer stated the way he ran the UK program was in great comparison to Germany while under Adolf Hitlers control, just on a smaller control & w/o the killings & racism obviously.
It's certainly not an uncommon thing, nor am I even saying having that type of influence is wrong if used correctly. If a person grows into a role of being in charge of others in a controlling dominance, I imagine it could easily become intoxicating.
So in short, walking away and giving up that type of influence, power, & and control probably isn't easy to do on your own. Often times it's got to be a forced occurrence. Tubbs may choose to coach until it's no longer a option & stops getting offers presented to him.