HID "bulbs" do not burn out in the way that incandescent (Halogen or otherwise) burn out. There is no filament that can fracture. However, there can be a failure at the anode or cathode, that can and does occur after some time. What I said above is that the NOMINAL life is about 12,000 hours (for me this equates to roughly 350,000 miles). What happened with your A6 was atypical of this technology and probably should've been covered under warranty.