I think the key is that, the machines that make extremely advanced machines are not that advanced in of themselves.

You don't have to go down that many layers from the machines that foundries use (arguably objects among the very apex of human technology) to bog standard fabrication machines like lathes and mills and whatever they use to cast metal. We have lots of those around the world. It will definitely take a bit of time, but I don't think it will be all that utterly devastating.