If it came to that, you would need to survive the first 30 days or so by staying hidden. The majority or our population would be dead by then. Very few folks would be able to revert in time to survive once known stocks of food and water are gone.
I am presuming that all utilities are also gone, meaning no or limited electricity or natural gas production. If that happened in the winter, it may not take 30 days.
I would keep a bow handy, for sure. Eventually, bullets etc will go away (although for some, that may take a while). Arrows can be made every day.
Oh oh, I gotta watch what I say or the Pres will see that as a great idea to control guns.....
Life would change, and maybe not for the worse.
CHuckC