1. Is it possible: Yes, possible but probably not real likely.
2. Why: Look at the burn rate of cash versus cash on hand.
3. Is it catastrophic: More perception than reality. Bankruptcy would actually be an excellent way to set wages and benefits at a level that makes economic sense versus UAW negotiations. In GM's case they would get out from underneath obligations for the Delphi restructure. In bankruptcy one can start over on most existing contracts; cancel for better pricing, switch to others with better prices and terms.
4. Other comments: The politicians will be manuevering all over the place to prevent any of this occuring. They don't like economic reality when it hurts their ability to pander to voting blocks.
If things get much worse, I could see either of the big two going chapter 11 just to get out of financial obligations or have them lowered to more attainable rates.
Chapter 7 or 13 belly up? No way. Only if the invention of the human teleporter comes out tomorrow.