He has all the leverage, but hey, we can do it without him, smh
The Cowboys could prevent him from playing almost indefinitely if he does not show up.
He is under contract for 2 more years.
If he does not report before game 11 of 2019, he won't accrue a season towards free agency.
Even if he made it past the 2 years and played just enough games to accrue time towards free agency, the team could then use the franchise tag on him for at least 2 more seasons.
He would not get paid while holding out.
If franchised, the tag amount would count against the Cowboys cap in the off-season, but if he didn't report that season, then the tag amount comes back off the Cowboys cap and they can roll all of that cap space to the following year.
FYI - Le'Veon Bell last the entire 14.5M franchise tag amount that he would have received for playing in 2018. Even after skipping the season, the Steelers could have Franchised him again. The contract he ended up getting was likely not much if any larger than what they would have paid him. It was less than Gurley's contract.