The reason why this is even a debate is because Dallas will potentially have a top 5 draft pick. Whenever you're drafting that high, you have a better shot if landing a franchise QB. And a QB of equal or better ability of Dak, on a team friendly "prove it kid" rookie 4-year deal, is worth it's weight in gold, because that capital saved by not signing Dak would allow the team more flexibility to sign other key FAs to help compliment the draft in fixing the other needs (especially on defense).
Now, on the flip side, especially if they win another game or 2 and end up drafting between 6-10 instead of top 5, I could also see them remain "all in" on Dak and use that pick on a franchise LT or on D. I honestly think it's a matter of where they are drafting. Win a few more games and I think Dak is more likely to come back; as of now I would already put the odds greater than 50% that he gets tagged.
Keep in mind that Dak was such a value pick in the 2016 draft. I would argue his numbers are better than Wentz or Goff.
But Dak at 37-40 mil/year vs. a guy like Justin Fields or especially Trevor Lawrence on a rookie contract? That's a tough predicament, especially for a team with so many holes to fill. Although I don't see Dallas being able to sniff Lawrence unless they overpay in trading up, and the draft gurus like Jimmy Johnson would argue that would be a bad move for a team with so many holes to fill.
I think a huge question needs to be asked: even with Dak, Dallas is a bad team, at least on defense. How long would it take to fix that defense, i.e. how many of Dak's prime years of what would be $35-40 mil a pop would be wasted in the rebuilding process? If it's going to take a few years or more, you might as well go into full rebuild mode with a 21-22 year old QB than 28.