Some electricity is not that hard to generate with late middle-age manufacturing techniques. It won't be a nice stable grid, but you'd likely be able to run e.g. mining pumps with power generated from a nearby water mill.

Similarly, some refrigeration is not super difficult to build once you know how it works. That would help quite a bit against starvation from bad harvests because it allows you to have bigger stores of food.

Solar panels and diesel generators are pretty ubiquitous these days. Actually building more of either is more complicated, but bootstrapping the capability to do so before existing supplies of either run out (and we're talking years here) is quite feasible.

You could scavenge electric motors, some metal sheets and a bunch of wood into a hydroelectric generator. So there would still be electricity.

Yeah, OK, I know how to wrap copper and spin it around magnets, and get _some_ electricity, but I don't know how to measure or manage the voltage and the current. I don't know how to make an inverter. I don't know how to make a light bulb or a battery (or really anything that "uses" the power). Exiting appliances only have only at most 20 years in them.

With everybody struggling to raise crops and livestock, let along trying to reinvent the light bulb, it would a long slow climb back to civilization.

> With everybody struggling to raise crops and livestock, let along trying to reinvent the light bulb, it would a long slow climb back to civilization.

People aren’t going to forget how to trade. The people with that manufacturing and engineering knowledge aren’t going to be busy with livestock. They’ll be trading these valuable goods for food.