First of all, congrats on surviving that. And I hope you at least got a some after all that.
Now on to the legal stuff, (I'm not a lawyer, but I do work in a law office and I'm in law school) I think that if you sue BMW there is a slight possibility you might win some money, or they might pay you just to close the case. However, you should know that BMW has very deep pockets - which means a legal team on par with the Yankees. If you (or your lawyer) can't prove the airbags would have reduced your injuries, then you WILL lose the case, and you will probably have to still pay legal fees. If a lawyer doesn't take your case on a contingency, he/she probably doesn't believe there is much of a chance in getting any money. Plus, if BMW's legal team were to search this forum, find your thread, etc... you'd be screwed, and they might even counter-sue.
I'd say be happy you survived. BMW might have saved your life, you shouldn't hassle them bc of the airbags unless they actually would have helped you. And it's been my experience that airbags usually hurt you more.