When will keyboard backlit lights die out?

Your computer will be useless long before the back light goes out, LEDs have a general life expectancy of 50 000+ hrs

Usually they don't die out unless the light tends to break ( doesn't happen very often )

25 years

As with any other light there isn't a definite amount of time for a light bulb to burn out. It depends on many factors. The answer could be anywhere from a month to 1,000,000 years.