So, magic.
And general idiocy. Firearms are not hard to reload. And are a far sight easier to use than a sword or a crossbow.
Ayup; and they're simple technology, too. We had rim-fire cartridges in the 1830s, and center-fire in the 1860s, and the only reason we didn't get them sooner was because nobody had had been smacked upside the head by the idea yet.
Even if computer-controlled precision machining is off the table, you could still crank out WW-2 era weaponry just fine with purely mechanical efforts, unless someone has also destroyed all the schematics and technical documents on the subject, as well as every machinist, engineer, and gunsmith that knows how to build them.
see the above mentioned starvation deaths....
Except for the fact that guys like that are the ones that would be smart enough to go find some Amish, or trade their mechanical skills to a farmer for room and board, or otherwise trade their suddenly-even-more-useful skills to help with their survival. That vastly reduces the odds of them starving to death, compared to the consumer class that only knows how to live inside the system.
Plus, a lot of engineers and such that I know of are in the SCA and other historical recreation groups, which means they have connections to a population pool that all have "low tech" know-how and advanced training with melee weapons.
Yeah, so do I. I'm in the SCA.
And, yes, our kingdom has a "rally point" for apocalyptic events. But that in no way means that any of us are guaranteed to make it there. From the mass rioting and looting, to thievery and murder that will be going on, to panic induced hysteria that turns even mild mannered neighbors into killers, most people haven't ever really thought out how bad complete anarchy will truly be those first few months.
And as a side note look around the SCA or other reenactment group, it's not like those groups are all filled with hardy/strong "live off the land" types. Yes there are those people in the organizations but they are the minority. And a lot of the ones with the knowledge aren't going to be able to use it because of infirmity or handicaps or obesity. Even the fighters, yeah they are big ass guys/gals and are strong, but a lot of them have bad joints now or bad backs, from the fighting. And evacuating thru a ravenous city that is congested with fleeing/looting people isn't going to allow you to take a big truck full of supplies thru all the traffic without being killed for your stuff. (or if we are still going with the no electricity, a horse cart) So if you are going to escape it'll be on foot or on bikes. If you're lucky on horses and people with disabilities aren't going to make that trek. Plain and simple, if you can't run you can't survive. The one really good thing is that these groups usually have a high number of gun owners in the ranks, with multiple guns. Carrying an arsenal would burden you down too much food is much more valuable at that point, so it's not like these people are going to go all "punisher" on robbers, they won't have the ammo for that.
This btw only applies to big cities and urbanized areas, rural areas and small towns should fare better, unless they are near enough to a large city to get overflow. So suburbs are done too.
Sorry. The point to all that is, Yes, there are people that do have the knowledge to survive but Knowing and
Doing are two completely different things. You are correct, after the frist few months when the biggest of the die offs are done those people with gunsmithing and machine-smithing skills can write their own ticket. But right now the fraction of people with those skills is really really small, less than a percent of the population. That percent will be even smaller after an event like this.
It would slow any rebuilding of stuff for a good long while.