I completely understand McCarthy's logic. The tripping call took us out of FG range, but there is also the consideration of where Detroit gets the ball. The Tripping call saved Detroit a TO. Had Detroit had only 1 TO left on that 2nd down call, I think McCarthy absolutely runs the football to keep the clock running on second down. Then again on 3rd down. That bad Tripping call really screwed Dallas and put them in a very bad position play calling and time-wise.
While all the talk is on the 2 pt conversion, that play never happens if the Cowboys are not called for Tripping when it should have been on the Lions. The Cowboys should have had the ball on the Lions 14 with a 1st down. No penalty call would have been better. Then the Lions are forced to use their second time out and Dallas has a 2nd and 3 at the 22. If They get a first down, the game is over. They can take a knee and run out the clock. Otherwise they burn off 40+ seconds on 2nd down and another 40+ on 3rd down. Then they kick the FG leaving Detroit with only about 20 seconds to go 75 yards for a game tying TD. That is virtually impossible.