Backup QB issue for Dallas?

It's rare that a team can lose its starting QB -- especially one that has invested a huge chunk of the salary cap in its starter -- and go on to big success that season, the notable recent exception being the New England Patriots continuing to roll with Matt Cassel after Tom Brady suffered a season-ending knee injury in Week 1 of 2008. As a result, the question of the need for a strong backup QB may be deemed moot -- after all, the ship might be sunk unless this player is truly a special player (and if he is, why would he be a backup in the first place?). However, this need is more important for short-term injuries, so the situation for the Dallas Cowboys behind Tony Romo is a little disconcerting.