A lithium ion battery will handle 400 daily charge (duty) cycles, which is about a year and a half, until it reaches 3/4 of it's original battery capacity.
1k lumens is bright, especially concentrated into a beam. 6 hours of battery, at what, maybe 2-5 minutes a day (more for those using it for work, biking, etc), you can see more than 400 days worth of duty cycles unless you throw it on the charger every day.
Personally, I'd probably get 3-4 years before it reaches it's 3/4 threshold. At that point, either something much better will be in the market, or I'll crack it open myself and replace the battery. It looks like it uses simple hex screws.
However... Would I be able to make sure I don't lose this $150 flashlight in the span of 3-4 years? Probably not...