You make a good point, it is truly a high risk - high reward scenario.
You dont pay Dak and he walks, you name Lance the starter and he sucks.................team goes from winning 12 games three consecutive seasons to a 5-6 win lottery team.
Jerry and the Cowboys will be the national laughing stock on every single website and news channel, they will all say "stupid Cowboys would not pay Dak and now they suck, LOL"
The opposite could happen, Lance takes over and is the real deal and is even better than Dak.
Its a gamble, a very high risk gamble because if you guess wrong it will set your franchise back for years.