I see lots of answers but I'll chip in. Compared to a typical incandescent bulb (including Xeon, Halogen etc.) a LED is essentially indestructible (note that is a comparison, not an absolute). Typical bulbs have very thin glass shells around them and contain a thin wire/filament that gets heated to produce the light. This construction is pretty fragile, at least compared to the rest of the flashlight and has a relatively short service life.

LEDs are basically a fancy transistor and essentially solid all the way through. For a typical LED "bulb" there may also be some additional solid state circuitry for regulating the voltage and current supplied to the LED. For a well made LED the life expectancy is measured in years (say 50,000 hrs) even with bumps and impacts. A well made flash light bulb has a life expectancy of around 5,000 hrs, assuming no rough handling.

In a nutshell anything that physically damages the LED will probably damage the rest of the light to the point that a replacement bulb won't help.

- Eric