Why would you walk away from one of the most valuable players in the league? Even if you're worried about him holding up long term, you can still trade him for high draft picks at any point over the next three-ish years (rookie deal, fifth year option, franchise tag).
If you have concerns about signing Parsons long term for any reason, that's the way to do it. You don't just let him walk to maybe get a third-round comp pick in two years.
Either way, I would expect Parsons to be a Cowboy until at least 2027. If his body starts breaking down by then, you'll know.