The only "leverage" they've ever really had, besides the franchise tag, is this misperception that the Cowboys are some dream destination for every NFL player. Jerry and Stephen still think every football player wants to be a Dallas Cowboy when they couldn't be further from the truth.
There is absolutely no way this works out well/good for the Cowboys. To keep him, they'll have to pay him a king's ransom and they'll never get remotely his value in a trade since he'll be on a franchise tag. Honestly, it's lose/lose unless you think Dak is truly an elite QB that can overcome a lack of depth and talent.