If the dealer insists on coming to get it, I'd suggest they bring a replacement light and install it and call it done. My vote for cause would be the reflector/lens unit clamped in slightly crooked or was overly tightened and was under strain. With enough heat expansion cycles, the strain made it break. I don't understand their "terror" of having you ride it. While your dealer may not have heard about this, there have been several reports in this and other forums about this happening. A long time ago, my dad told me that with any mass produced item, if something happened to mine, it likely has happened to lots of others. That holds true with this problem also. This will test your dealer as it will be easy enough for them to claim some rock chip you didn't notice weakened the lens and they won't cover it. If they do cover it, especially without an argument, you chose well.
Keep in mind this wasn't just the bulb. It was the outer glass casing. The glass hit my garage door 10 feet away.
This same thing happened to my buddy recently on a Street Glide. We were on a trip with the bikes parked on a ferry. We came back about 4hrs later and the glass from his left passing lamp was just laying on the ground in front of the bike??? We were so confused as it was not an area which anyone would be walking by. And this is Japan...people don't go by and just bust people's lights for no reason. Not to mention my limited was park right behind his as well as other bikes behind mine.