I searched around on the Cree XR-E (the LED used in the LX2) and found the link below regarding lifetime prediction. If you look at the top of page 7, it shows the lifetime chart at varying temperatures with a 700ma drive level (close to the high mode on the LX2). The measurements are in Celcius, but pay attention to the ambient air temp more so than the junction temps. 45C = 113F, 85C = 185F.
This means that, as hot as it could possibly get in most geographical locations (113F), absolute worst case scenario is your LED would burn out after around 90,000 hours. To hit that mark, you'd have to run the light on high for 10 years straight. You'd go through 90,000 CR123 batteries at a cost of $1.50 per battery which comes out to $135,000.
http://www.google.com/url?sa=t&rct=...KUzV3o8XM3bGn51V3e2o_lA&bvm=bv.75774317,d.aWw