I could understand the skepticism if we were talking about Aikman, but we're talking about a first-year starter and a coach who might be making his final trip to the playoffs.
Admittedly, this is a worst case scenario that noone including myself wants to see, but I don't think it's as inconceivable as everyone would like to belive. It's the playoffs, the goal is the super bowl, and if Romo has 2 fumbles, 2 ints, and a 30% completion rate and we still have a chance to win the game I don't think Tuna would hesistate to go to the bullpen.
As for wounding Romo's ego, I don't think that's really concern as he seems to have a fairly healthy opinion about himself. I'm sure he would recover form a benching just fine. Drew, on the other hand, might be ruined from what happened to him earlier this season.