But when supplies run out the idea is to restore manufacturing ability. It's hard to bootstrap 7nm fabs in a Mad Max wasteland but we might conceivably be able to get back to 1980s tech.
You can get back to 1980's tech easily enough if you have 1970's tech. And so on all the way back to about 1920. Whatever you have + the knowledge remaining will allow you to rise up the ladder a little quicker but not that much quicker because you still need to go through all the motions in between. Skipping steps is really hard, most progress is incremental.