"Back in my day..." we had registers that held the money that customers exchanged for the goods. Servers could write down orders on small pad and hand it to the cooks. There were lots of ways to not close your business because the phone company wasn't working. The move to cashless society has many pros/cons, and this is just showing a glaring item from the cons list. You live by the sword, you die by the sword. Some of us prefer some shields and armor though

Edit: it's so ancient that even I nearly forgot about them, but credit cards used to work by having the company take an impression of the card, then send in the receipts. sure, it might take a few days for transactions to complete, but it worked for several decades. there are fallbacks available to us, if we would just decide to allow for it rather than just failing