I would imagine it would be very difficult to convince a promising manager like Rowett that taking a coaching job with us is the best way to progress his career in management. I'm sure he would take the manager's job if we offered it to him but a coaching role? Not a chance. Nothing in it for him but money which he doesn't need.
I don't see why he wouldn't do it, on the condition that he was free to move if offered a manager's job elsewhere. If he does well it could enhance his reputation.