It depends. LEDs use current-regulated power supplies. Lets say your bulb had two chains of eleven LEDs in parallel. When one LED burns out the whole chain i

It depends. LEDs use current-regulated power supplies. Lets say your bulb had two chains of eleven LEDs in parallel. When one LED burns out the whole chain is lost and the regulator would increase the voltage across the remaining chain until it was using enough current for two. Naturally this will greatly shorten the life of the remaining eleven LEDs. This is the worst case scenario and probably won't happen. Two ways around it. 1) Since current is (non-linearly) proportionate to voltage, the regulator need to increase the voltage to compensate. But all regulators have a maximum output voltage. If the regulator is cheap and running near its limits, it can't increase the voltage high enough to damage the remaining chain and the bulb will run a little hot but be fine. 2) LEDs get warm and should not operate above 85C. A good regulator has a thermistor connected to the LEDs and will automatically drop the current to safe levels. The bulb will once again run a little hot but will be mostly fine. If there are more than two wires connecting the regulator to the LED it might have over-temperature protection. Or if the regulator is physically connected to the heatsink. The regulators themselves are pretty reliable. I work mostly with low voltage DC lighting (12V-48V, 20W-100W) and there is nothing in the regulator that would wear out easily. Line AC might be a different story, those probably have large filtering capacitors. If the caps are electrolytic they might dry out eventually from the heat.