Oh come now -- Lenny Wilkens would be as good as any and better than most as a "wise old head" you could get to sit next to a raw rookie coach who hasn't been in the NBA for 20 years. The position is almost by definition limited to guys who are washed up, and you want the guy to be low key and low maintenance.
But for Lenny himself I see no way he would want to come in and serve UNDER Reggie Theus. He just got done being humilaited by being supplanted by a 30 yr old GM with no experience in Seattle, and clearly chafed at it. Now at age 70 whatever he's going to come back to serve as an assistant coach under a noobie head coach in a small market city where he has no ties? Don't see it.