Very worried. It's definitely one of the reasons the stuff is so cheap. I do have faith that SOMETHING reasonable will always be available. I'll initially try to stock up on popular bulbs that are still floating around and see how long I can push it out, but even now theres a bulb by reef brite that I think is fine and still in production so I can keep my eyes on it.
My other choice for lighting a 6' x 3' was to get 4 of the XR30 blue knockoffs. However, those are like $180 each new. Metal halide seems to make a lot of sense to me right now even if there's an end date looming.