Is that a serious question? Or are you merely playing Business Advocate? Of course GM's owners are going to try to make the employees pay for their loss in profitability, and of course the union leaders are going to be under pressure to allow this to happen. But since when did we simply accept that state of affairs? Redistributing wealth to the owners and away from the workers - which is what this deal entails - will surely enable them to find more ways to invest in cheaper offshore labour and factories, (which is why they have given no commitments on that question). If you're a working class American, you may as well push for your share now, because anything you give them will be one more resource with which to deprive you of future work, entitlements, healthcare, wages, etc.
So, assuming I were in a position to do so credibly, I would have proposed a grassroots militant campaign to oppose the whole idea and tell the owners to pay the bills with all the billions in cash that they have made off of our labour for the last thirty years. The way you've phrased the argument suggests that you would have opposed militant strikes in the 1930s because the bosses were too poor to pay out due to the crisis.