If they do not extend Dak, then be prepared for a few years of misery.
First, they are projected to be over the CAP next year as it is. So they will need to make room somehow just to get under the CAP. Then they have a bunch of free agents they need to sign. They are not all great but they contribute to the defense. If they are not resigned JAGs will have to take their places. In other words, if they do not extend Dak to free up CAP room, be prepared for some losing seasons ahead just because of the talent they will lose and be unable to replace. Then when Dak is gone, it gets worse because they will not have a QB - unless somehow Trey Lance emerges to become something he is not right now. The time to bite the bullet with Dak was his last contract. Jerry never should have agreed to give him $40 million unless Dak was willing to make it for at least 6 years.
Keep in mind the Cowboys traded away their 4th, 5th and 6th round draft picks so re-tooling won't be easy either.
Maybe it makes no difference. If you believe they cannot win with Dak then what's the point of keeping him? Cut his contract and lose without him. But then who do you blame? The Cowboys success drafting players like CeeDee, Diggs, Micah. and even Dak means they have to pay for that success, which is the problem with the NFL salary CAP that penalizes teams that draft well.
The Cowboys are going to extend Dak because they really have no choice. The first time they resigned him they gave away all their leverage then pushed his CAP problem into voided years. At this point, they probably have to re-sign him.