If you read the article I linked above, you'll learn that in the event such a mission is required, the doomed ship will be allowed to fall to Earth to be destroyed in the ocean, instantly eliminating one-third of the entire fleet and effectively shutting down the shuttle program forever. As a die-hard space nerd I never thought I'd say this, but the entire program should have been scrapped decades ago.
Imagine you bought one of the most expensive, most technologically astounding cars ever made, one with millions of intricate subsystems that all needed to function in concert to keep the beast lumbering down the road. For the first five or ten years, the car would most likely run beautifully - not unlike older-model Jags (made before Ford bought the company), which were amazing cars but were so incredibley finicky and complicated they broke down at an amazing rate - but after two or three decades, even with incredible care, there would come a time where the poor thing would be so beat down and dangerous that you wouldn't dare drive it.
I realize that government money, especially at NASA these days, is tight, and I also realize that the U.S. has made quite a committment to the ISS which requires the shuttles be in operation, and I also realize that the Space Shuttle program was designed to be re-usable, but so are my contacts and eventually there comes a time where I can't see a damn thing unless I throw them out and get a new pair. Surely someone on Capitol Hill or at NASA has thought that instead of wasting millions and millions of dollars on a failing and amazingly dangerous (both physically and politically) program they could divert some of that money to the development of a modernized space vehicle that is actually modern. Don't get me wrong, I really do love the shuttle program and I have been a space dork my entire life, but the 1960s really were forty-five years ago at this point folks; it's time we started thinking about space in terms of 2005 and beyond and not in terms of the last millenium.