I dont know if Diaco is ready yet to be a head coach. He's a great defensive coordinator, but still very young. I feel like he has much to learn, especially about offense, I think that was the point of making him an assistant head coach. I think Kelly will spend the next season or two tutoring Bob about offense, and the subtle details of being a HC. His potential is through the roof, but he needs to be ready.
Kiffen was a great OC under Carrol, but he went big too soon. If Bob is to leave, I want him to be succesful, I think he could use a few more years being tutored by BK.