.. .so in this case it probably won't ever get there.
The Post office is broke, or is at the very least on a trajectory to 'broke'. It's losing money hand over fist for all the same reasons that all the other union dominated defined benefit pension entities are going broke. But in this case we can be certain that no one is going to care. The secret to this is in the otherwise enlightening WSJ editorial describing the problem:
The Postal Service repeated on Wednesday that without congressional action, it will default—a first in its long history, a spokesman said—on a legally required annual $5.5 billion payment, due Aug. 1, into a health-benefits fund for future retirees.
There you have it. The people who aren't getting paid are 'future retirees'. So money they are being promised in their fantastically generous union contract, is not getting paid and when they need it ... it won't be there. This is, ironically, exactly the same position that we private sector people have been in with our federally promised 'future benefits' for a few years now. So in some sense you can think of this as the Postal worker's unions taking on a 'shared burden' or 'paying their fair share'.
Nice to see that they're walking the walk, even if they don't mean to.