I think a GM has to have no regrets. If they offer Dak a fair deal, or at least a deal they think is fair and he rejects it then the answer is not to offer him more and more money until he finally signs. That is stupid no mater who the player or what position he plays. At some point the Cowboys will draw the conclusion that Dak is not interested in playing for Dallas - if he refuses to sign a reasonable deal.
Whatever regret the Cowboys have it could be short lived if they get 2 first round picks and find another QB. It will be short lived if they sign a good QB and also rebuild the defense into a squad that actually helps win games for a change. But in the end, if Dak refuses to sign Dallas has to forget about regrets and move on.
Maybe it will be Dak regretting not signing a deal with Dallas if he goes to a small market team and loses all his endorsement deals.