The problem is the "reduced pension liability" is no longer UA's liability, but shifts to the US Taxpayers.
We've seen this happen with: Bethlehem & Republic Steel, Delco, parts of GM etc. etc. and more recently cities and municipalities. The Taxpayers should be able to say OK, if you really can't pay, we'll help out BUT, if you (UA) subsequently recover, pay the Taxpayers (PBGC) back, AND pass that new found success on to the retirees!