Comment by RetroTechie

In case more advanced nodes would disappear, even a semiconductor factory capable of producing eg. 200..500nm structures would already be very useful.

Remember the first 32-bit cpus were manufactured on >1um processes. Never mind 8-bitters or KB-sized memory chips.

Also note that IC designs, assembly programming & more, can be (and has been) done by hand. Having any kind of compute, no matter how slow by today's standards (couple MHz) helps a lot. Same for basic applications like text processing, spreadsheets, small databases, software development, etc etc.