An under-fed incandescent could last centuries. However it would waste 95% of its energy as heat instead of producing light. That's actually not much of an issue if you either live in a cold climate and the heat is useful to you, or if the light is only lit on occasion (attic, cellar, closet ...).
My wife and I were talking about what lamps we had that were LED vs fluorescent vs incandescent; one of the bulbs that we have that is of the latter is in our closet, and has been there since before we bought the house in 2002 (the house was built in 1973).
18 years now, maybe longer, but it still turns on and has yet to burn out. Of course, we don't use it much, and it's only something like 30 watts (clear bulb).
