I don't think Jerry can stop any coach from leaving for an advancement...it's not just for being a head coach. If you are the secondary coach and have a chance to become a coordinator, you don't need anyone's permission.
I don't get all the wringing of hands over these guys. Except for Garrett, every coach here is a holdover coach from Parcells days, from days when we all thought coaching was subpar. When I see Newman and both safeties going to the pro bowl and Henry having one of his best seasons with Dallas and Reeves having some good games as the 3rd corner, I personally have to wonder about the coaching of the secondary that seems to be our achilles heel. Other teams have secondaries with no one going to the pro bowl and yet they perform better.
Any coach can be replaced, and we might even be better for it. Wade's been around for a long time, and he seems like a good guy to work for. Good coaches should see Dallas as a place that is winning, has good players, a loyal owner who will spend money, and a great opportunity to advance their careers under a head coach who due to his age isn't going to be around forever.
I'd hate to see Garrett leave this offseason, but even if he does, we'll still be fine next year...as for all the position coaches, I look at it as good for them and a chance for us to possibly improve with some new blood.