In a way, Cuban is indirectly responsible for all of this, as I doubt he would sign off on this if he was still majority owner, and it might not have happened if he had sold to someone other than Adelson/Dumont. It seems pretty clear that the main goal for Adelson/Dumont is to get gambling legalized in Texas, and build a casino/arena resort for the Mavericks. Winning championships is a secondary goal.
In another thread, I said that I thought the "Mavs to Vegas" idea was crazy, but the more I think about it, this may not be so crazy after all. There has been little traction in legalizing gambling in Texas. Even if the legislature could be convinced to pass a constitutional amendment to legalize gambling, it would also have to be approved by the voters, and now you have a voting bloc in North Texas that might vote "no" simply out of spite.
If Adelson/Dumont see the writing on the wall that casino gambling isn't going to be legalized in Texas anytime soon, they could potentially try to buy out of their lease with the AAC, which currently doesn't expire until 2031. If they could find a way to break the lease, they could move the team to Vegas and build a casino/arena there. The NBA doesn't currently have a timetable for expansion, but they won't wait forever to get a couple of new teams in the league. If Adelson/Dumont moved the Mavs to Vegas, North Texas would move to the top of the list of expansion geographies, and it would likely be pretty easy to find a qualified buyer in the Dallas market that could care less about gambling and would simply want to own an NBA franchise.