The Cowboys purposely structure their long-term contracts to allow for years like this. I'm not saying they will do it but Smith, Martin, Zeke, DLaw and (to an extent) Cooper's contracts were designed to create win-win scenarios whenever the team needs cap space by paying out guaranteed money ahead of schedule in exchange for a lower "on paper" salary.

The salary cap is far more fluid than it is made out to be, it's not a clear cut " you get x amount of dollars each year" situation. It can be worked in several ways to essentially move money around, roll unused cap into future seasons and/or "borrow" from future seasons at what amounts to negative interest assuming the cap continues to go up from year to year.