If GM goes under it will be a massive disaster for everyone, not just BMW. While I have always thought GM was a mess, the fact is they are such a huge part of the entire delivery infrastructure of our country. GM provides a majority share of parts and vehicles for just about every delivery system in the US. Now imagine, parts and vehicles for all those companies are no longer available or in short supply. The effects would eventually be overcome, but it would definately be long term and more widespread than most people realize.
That's just the delivery systems - think of all the emergency services as well.