The LED should be expected to outlast the rest of the phone by a large margin. That said, given enough units out there, it's statistically inevitable to get a couple with some issue that die earlier.

If phone manufacturers cheap out, they can fail to handle the heat from continued LED use (e.g. as a flashlight) which can cause premature failure

No but I did have a flashlight fail me while I was exploring a long abandoned power plant and in a dark room with evidence that someone may have been living in the facility. I only shit my pants a little

I think it only fails on horror movies other than that i have never seen one fail IRL.

I once got a „refurbished“ phone from a third party shop where it was not working. But I guess it was a defect from the refurbishment itself. They repaired it though.

Other than that, no. And I don’t think the LED would fail, maybe the plug would rattle loose.

Fail as in did not provide enough light to walk through the woods, then yes. I have flashlight in my EDC.

Now I'm curious as well. I use it often, but not for that long each time. I know it gets hot after a while and it drains the battery.

How long is it supposed to last?

No

Yes. Samsung S6 edge I think? Before flashlight was an intentional functionality. I had an app or a ROM that gave me a flashlight button but if I used it too long it would stop working for a while. It would come back eventually but made me nervous so I avoided using it for more than a few seconds.

No, at least not independently of other hardware failures.

If you mean the screen, then yes.

no but I have often thought that it would be a good thing if it did because I hate light