Ultimately, ATSB pulling the plug will not change too many votes... For one, Joe Average Voter wants cheaper fares, and is not overly concerned with the fate of 28,000 employees. Furthermore, US Airways 28,000 employees translates into maybe 100,000 voters (including spouses, retirees, and sympathetic family members, etc, not all of whom will vote). How many of these people will change their vote based on the ATSB decision? Some will, but certainly not all.
Regardless, it is the ATSB's job to protect the best interests of the federal government. The best interest of the federal government is probably to stop supporting failing businesses and stop perverting the capital markets (How many other airlines cannot get, or get less private financing if the government continues to support a failing US Airways?) Certainly, any further investment in US Airways by the federal government will ensure the continuation of "excess" industry capacity, low fares, and loss producing companies. If the ATSB continues to allow US Airways to flounder, then all airlines will be hurt and the industry could collapse.
Also, and obviously, it is not in the government's best interest to invest more in a company which has not been able to demonstrate any financial turn-around. It is probably in the government's best interests to get its money out of the situation, and let the free market work.
While US Airways failure will not "fix" all the industry problems, it will help reduce capacity (i.e. supply of seats) and help prices and revenue at the remaining carriers to rise.
While this is little consolation to the employees who face hard times, its not in the government's best interest to continue to subvert the capital markets.