Except this article is specifically about solid state components failing in a much shorter timeframe.
Most modules with flash in 'em are programmed once at the manufacturer, reflashed once or twice during assembly, maybe reflashed once more at the dealer before delivery, and that's it. Maybe again post-sale if there's a recall or TSB or something that can be fixed in software.
Flash quite happily lasts 25+ years if you don't abuse it far beyond any flash manufacturer's wearout specs. Go figure!
concievably a big capacitor or watch battery could keep a 4 or 8k RAM going for quite a long time.
For Toyota ~57 million vehicles from '02-'09 https://www.toyota-global.com/company/history_of_toyota/75ye...
For Honda ~23 million from '02-09 https://www.statista.com/statistics/267276/worldwide-automob...
Volkswagen group looked to be in between the two.
Didn't look for Ford or GM.
To say that there's "tens of millions" of perfectly operational cars on the road in the US is really an understatement.
Spare (electronic) parts shouldn't be an issue with major brands. I've seen the same sensor used on a dozen models from several manufactures produced over 10+ years. As Takata exposed, there aren't that many parts suppliers around the globe, so a lot of commodity components are shared across the industry.
For long-term part replacement, I'd be far more concerned with construction techniques like plasma-transferred wire arc sprays used for creating cylinder linings. This technique cannot be replicated outside of the factory, thus, they kind of make engine blocks disposable (they can be sleeved, but they won't perform the same and will require different piston heads).