The probability of Gruden coming the Vols is less then 1%. Think about it, the 10 highest paid coaches in the NFL make between $7.5 to $5.5M. If Gruden were to coach again, I would believe he would become one of the top 10 highest paid coaches in the NFL. The Vols can't pay him anywhere close to that and pay his assistans the salary they will require to come here.
I have many other points I could make but chose not to piss on anyone's parade.
Read this article on his wife, pretty sure she wouldn't want to come here either.
Life With Gruden for Better or Worse - SFGate
We can all dream for a big time coach like Gruden but really need to be realistic.