Remember, I'm a chemist-I'll make my own gas
I don't see IC engines going away COMPLETELY in my lifetime(although I could be wrong)-I suspect industrial/heavy machinery/etc will keep them around for a while. Heck, there's still a lot of steam in service in marine applications(although AFAIK not reciprocating engines outside historical applications) and new nuclear subs and the like are steam that uses a nuclear reactor for heat rather than an oil or coal fired boiler.
In any case, I suspect the ability to machine parts will be around for a while, and there's a fair bit of old stock still on a lot of this stuff.
As you say in around about way-specifically about hybrids but it also applies to modern full-IC vehicles-if an electronic module dies you can be dead in the water if you can't find a replacement, or at least it might be prohibitively expensive. Several years ago, my dad had a pickup truck(mid-sized Nissan, whatever model it was) eat two ECMs, fortunately under warranty. The first happened when I went out to drive it one morning and it would crank beautifully but not fire. I tinkered with it and got it to cough once on ether, but I dug a bit more and was only getting an occasional spark and there was absolutely no pressure in the EFI rails. It got towed to the dealer, who ended up having to send it to another dealer, and finally got an ECM. Two weeks later, that one died, and the same adventure ensued(I think they found a different module that was misbehaving and causing the ECM failure, but don't remember the specifics). All said and done, that was about $6K of warranty work, and he traded it in a month after all that was done.
The older a car is, though, the easier it tends to be to keep going. My mechanic fought for a while getting timely work done on flatheads at machine shops, so he finally bought a mill to at least skim them in-house. He doesn't have the ability, or the time really to learn, how to do a proper valve job on OHV engines, but flatheads are probably 50% of his old car work. He still has to send blocks out for boring, but can at least skim and do valves on flatheads. He pours his own babbit bearings too, which covers most turn of the century up to probably 1940s stuff. Of course, he won't be around forever, and there's still stuff that's beyond him. He has a big 1930s IHC flatbed truck sitting behind his shop, and he may never get it running again since pistons for its big I-6(I'd guess probably 6-7L from looking at the block) are unavailable even though it's otherwise prepped and ready to go.
