Update: Either there have been recent developments or my email started something at the ISP level. The webpage now simply states that the company is out of business. I did some more digging and found that they are part of a parent company in Canada that produces batteries, Infinity Trading Company. When I called a phone number listed for the General Manager, the other side responded "GS Infinity." I asked if they were still associated with Nite Hawk lights or if I had a wrong number, to which he stated "Wrong number." I looked up GS Infinity and they seem to be a company in the same town in Canada making (surprise) rechargeable batteries. It sounds like they started up the bike light/ headlamp business to move batteries but it didn't provide as much as they wanted so they shut it down. I can't say when that happened but probably earlier this year. All of the links to the site have gone down so I replaced them with ones from the Internet Archive's Wayback Machine. And yes, I guess I do have too much time on my hands.
Update #2: There are still a few businesses out there still selling Nite Hawk lights. The only one I would really trust would be www.batteryspace.com, and that's not from personal experience but just from noticing that they are selling them with a batterspace battery and charger. They should be able to warranty that.