These extremely experienced people are recommended to people that do not want to attempt their own repairs and are looking for the BEST and most likely to be successful repairs.
There are loads of people attempting and often enough succeeding at their own repairs, as evidenced by there being several extensive online resources (websites, youtube channels...) dealing with camera and lens repair. Not all of the authors are of older generations. And given that it is likely the exception that someone is willing to both learn camera repair AND document it online, there will be far more people that know something about it. Also evidenced by activity in big forums - questions for repair advice are often answered. Also, while these might be bootleg copies, a lot of manufacturer repair documentation (service manuals) has leaked into the open internet.
1970s and younger cameras using true custom electronics parts will probably be the most problematic someday: If you look at the integrated circuits used, a lot of them seem to have been designed for exactly one camera and manufacturer. Since there was no intent to market these parts alone to anyone else, and since even authorized repair facilities weren't meant to use these parts for new designs, there hasn't been any public offline or online documentation (databooks and datasheets) ever. Even a person extremely skilled in electronics, but without a spare integrated circuit at hand, would be forced to essentially redesign the circuitry around available parts.
A mechanical part could almost always be replicated by a skilled machinist - and some of these will always be around since you do need them for prototyping in science, research and design...