Great news. It would be nice to actually see a big company fail. Currently, GM bonds trade at an average price of 18 cents on the dollar. This would not shock financial markets. Anyone lending to them already has taken a big hit. The stock trades at a value of $1.7B, on $91B in assets--option value. Implied vols are around 220%, the short rebate is about -87% (you pay 87% annually on the proceeds generated from a short sale).
Thus, it's already dead. Bankruptcy would not 'disrupt' the firm, it would clarify the situation.