The graybeards are aging out, nobody compiles their kernel anymore, and someday something deep will break and there will be no one left who can climb down and fix it.

I dunno. I suspect it'll be slightly different in the OSS world[1]. There will be some folks who can climb down there and fix it, but since that skill is no longer valued (as in, being able to do that isn't valued by most users now, much less in some hypothetical future). And they will be expected to do that, now, without thanks. And when they say "I'm too old for this shit...you can go pound sand" because this was one unpaid insult too many, users will shrug their shoulders and load windows or buy a mac because those companies are paying & tasking people to keep things running. And by inches oss ceases to be a thing.

[1] Yes, I know there are many oss devs who get paid for their work. Many critical contributors do not.