To answer the question, defenses change in the last two minutes, or late in the game. It depends on the situation. Against Detroit, the Lions had no timeouts left. So Dallas allowed them to throw passes over the middle thinking that every completion keeps the clock running and eventually Detroit would run out of time outs. But with 1:40 left in the game this makes non sense since they could easily run enough plays to get down the field and stop the clock with quick snaps and throwing the ball into the ground. This is why McCarthy calling pass plays on the Cowboys drive was so stupid. If they run the ball they take another 45 or 50 seconds off the clock and the Lions would not have had enough time to use the middle of the field. Of course they could use the sidelines and go out of bounds to stop the clock. But the defense would play outside and try to force everything inside then prevent the receivers from getting out of bounds.
Dallas played very soft on that last drive and more importantly did not bring any pressure. Maybe if they threw a couple of blitzes at Goff they would force a mistake, or get a sack to run the clock and stall the drive. I think the best way to kill those late drive to tie or win the game is with pressure. I know it's a risk, but that is the Cowboys defense. It is how they play best. Get so much pressure on Goff he can't find the open guy down the field.
That last Lions drive was one of the most disappointing aspects of the game. If the Cowboys didn;t get lucky on that 2 point conversions we would be talking a lot more about how they allowed that drive at home.