I would want to kinda keep Kubiak for at least one more season. Its more for Spencer Rattler than anything, I wouldn't want him having 2 offensive coordinators in 2 years. He would be learning a new system which would make him a Rookie QB again.
My only knock on Kubiak is that his creativity comes in spurts, he runs a play I've never seen before then when 3rd and long comes, he calls the most boring predictable play ever.