The longest I have noticed so far, Christmas LED lights, is around 5 years and still working. The benefit of using LED lights are cost effective as they consume very low energy compared to incandescent bulbs.
Either you replace or buy new, always use LED choices.
Speaking of LED lights, btw, I’ve been replacing most of my regular lights with LEDs, and they’re really fantastic. Especially the candelabra lights–they’ve really come a long way. Just bought these yesterday:
Only thing I don’t like is that I see starburst when I look at LED lights. Not a big deal around the house, but cars with LED headlights really drive me nuts. But I do wonder whether an entire string of LED lights on a tree would drive me crazy.