Will assume an advisory role with the AD. It seems odd, unless he's just burned out. He'd make someone a really good hire if he decides to come back.
Maybe his plans for a national championship never materialized, and he realized the challenge after playing Bama in the playoffs one year. Maybe he found it too challenging to go undefeated every year in a "Big Boy League" (the PAC12
) Maybe he was knocked off his soap box....
Probably undisclosed health reasons.
Best of luck to him.