If I stretch I guess I can see why your asking this question. However it really is kind of close to a doomsday type question and those threads get closed pretty regularly here.
The obvious question is, if you envision having to make your own black powder, what are you going to do for primers? If your going to stock up on primers then why not go whole hog and get powder, cases and bullets too?
A good place to start answering many of your questions might be a reloading manual like 'ABC's of Reloading".