The visiting team has a huge disadvantage playing on Thursday night especially this late in the season. The Cowboys are the better team and given the situational circumstances, I see Dallas winning by more than a touchdown.
Don't be fooled by Buffalo's 8-3 record. It's bogus. The Bills have played opponents whose combined record is 19-53. They haven't faced an offense the caliber of Dallas. 
The Bills rank third versus the pass, but are just average versus the run. That makes them vulnerable to Ezekiel Elliott. He should be in line for a big game, which in turn would make Dak Prescott very effective picking his spots. Prescott has three quality wideouts plus Elliott out of the backfield catching passes. 
Buffalo lacks explosiveness on offense to keep up. The Cowboys rank in the top-seven in total defense and scoring defense. They are extremely well-coached on the defensive side of the ball. I wouldn't be surprised to see Josh Allen make a lot of mistakes in this matchup.