Do not take for granted that (hypothetical) Treasury purchases of newly issued GM stock would significantly change the organization of the industry by reducing the probability of bankruptcy. Absent Treasury action, GM would likely end up joining with another automaker. All the Treasury action might do is let GM be the acquirer rather than the acquired.
There are fraudulent conveyance laws: GM cannot sell its valuable assets and then declare bankruptcy. Thus, Treasury cash would enable GM to spin off GMAC only if GM kept enough of the Treasury cash to avoid going bankrupt too soon after the spin off.
If bankruptcy were the only way shareholders could free themselves from obligations to unions and retirees, then bankruptcy may happen regardless of whether the Treasury gives cash.