It would practically redeem them in the eyes of their fans.
You may not believe this but there was a time when the only thing better than beating the Cowboys was a Super Bowl. George Allen made sure we hated them just as much as they hated us.
The rivalry may not be as strong but I guarantee the most vocal Washington fans are the ones that remember the past bloodbaths. The animosity is cemented in a violent, ruthless, merciless, entertaining history.
Washington knows and we should know that if they win, it's another notch in that NFC East tradition.....If you can't win it, take a division rival down with you.
Your team could be defending SB champs and the other at the bottom the league and it wouldn't matter. If your team isn't completely focused, it's an "L".
Any Cowboys fan is going to have a mental list of the Washington Don't-say-my-name games in which a last second play determined the fate of both teams.