I will grant you that Dallas holds all the cards and all the leverage with Dez, and that realistically if Dez could be controlled and effective, that this is probably as good of a situation as the team could ask for.
On the other hand Dez was a perpetual problem, and consistently underachieved and would pose a locker room problem for the team. Why would a team do that to itself?
I personally think that ship has sailed. Then again, never say never with the Cowboys. Everyone would be talking about it.
If winning is your goal, then don't bring him back for any price. If making money is your goal and winning is irrelevant, then I would say there is some chance he could return.