Thanks to all for your input - sounds like an airbag only deploys if there's an impact at the side / end where the airbag is located. If I understand correctly, the rear hit would only deploy front airbags if the front end had slammed into someone else? This happened several years ago, and I've never understood why none of my airbags deployed, but the drunk driver who hit us had the benefit of his. The force was severe enough to give me a whiplash and others some lasting damage. As for insurance, not much luck there. The driver carried a minimum, and I had to sue my own insurance company. I never received a penny beyond fixing my X3, and they refused to fix a few things at that. (For instance, a front light bulb was knocked out to dangle against the reflector lens.)
Incidentally, I don't believe we would be alive if it weren't for the DSC - I wasn't able to control it, but my car managed to stay on the road without even spinning!
Thanks for all your input, and I'll get the dealership to look at my passenger airbag & light.