Even if UAL were to get out of its pension liabilities, the effect would only be 75% as bad as it sounds. BTW, USAirways got permission to drasticaly change its pensions just two days ago.
In the USA there is a government body named the Pension Benefit Guaranty Corporation which takes over the pension liabilities of terminated pension schemes.
http://www.pbgc.gov/
The problem is that some of the UAL people would get as little as 25% of the pension they were expecting.