Dak will be around at least 5 years. He will get an extension after this season, with at least 2 more years of guaranteed income, simply because it will be cheaper to sign him next spring than after that if he grows into a legitimate long-term starter. So, the first "out" for Dak will be after the 2020 season.
As for Jerry and Stephen, they SHOULD be praising their own players publicly. Any discord should be handled privately. I don't understand why anyone would think it is appropriate for an employer to publicly humiliate his employees. Of course Jerry and staff are going to find the good things to talk about publicly, and mitigate the bad things. It doesn't follow that they are unaware of issues, and are leaving them unaddressed.
I think the ones with mental instability are those fans who DEMAND that Garrett, Jones et al be as publicly critical of their players as some fans are. Even if the Cowboys want to move on from Dez, there isn't a scenario where it would behoove them to publicly denigrate him, or any other player. Like it or not, Dez is the leading TD receiver in DC history. They should (and we should) appreciate and value that - no matter your current opinion of him. Likewise, Scandrick gave the Cowboys 10 years of his prime athletic life. Although he was never a Pro Bowl player, he was a valuable member of the team. There is no reason that the Cowboys front office or coaching staff should EVER have anything bad to say publicly about players who've made such contributions to the team.
Heck, even with marginal players like Lucky Whitehead, the Cowboys were very careful to not bad mouth him publicly, opting instead for a simple statement that the Cowboys made a decision in the best interest of the team. They steadfastly refused to bad mouth Whitehead, even as he was badmouthing the team after he was cut. That is called being "professional." I don't understand why fans want Jerry & Co. to "open up" and share their raw feelings about players. That's NEVER a good idea.