oh yeah, PBGC

I have actually visited the PBGC (Pension Benefit Guarantee Corporation) before. And most of what we talked about was actually the chance of GM defaulting on its obligations. I forgot about that as I formed my thoughts on how to handle pensions in case of a GM bankruptcy. In principle, pension funds are in a lockbox so even if a company goes bankrupt the pensions still get paid. The problem in GM's case is that accounting laws allowed them to massively underfund the pension. IIRC, their annual statement mentions something like $30Billion in off-balance sheet liabilities for this. The PBGC is a government insurance company that takes over the pension fund in case of GM bankruptcy.
Those workers made a deal for less wages back then to get a pension now. To not pay them would be a crime. And honestly all the living ex-CFOs and ex-treasurers of GM should be jailed for life if that happens. But PBGC will ensure that the promise is lived up to to a large degree.
Here's a not bad article on the topic of GM bankruptcy.