Businesses or anyone wanting to get paid will figure out an alternative. Dealing with cash is not complicated.
2 hrs later, the regional manager - WHO HAD TOLD US IN NO UNCERTAIN TERMS THAT WE HAD TO REMAIN OPEN DESPITE NOT HAVING POWER - came in and chastised me for 1) not wearing the full uniform (we had no AC and it was July, so I took off the tie) and 2) handling money without a register. "You can't guarantee your numbers are right - that's what computers are for". "But... they're down, and you said to stay open and keep selling". "That doesn't change the fact that you might be making mistakes!"
Insanity.
Cards require a machine, some kind of network connectivity, and an account. It's actually a lot easier to deal with as a small business. Most of the people I know who go to conventions as vendors prefer cards because it greatly simplifies their logistics.
In the case of getting paid something versus getting paid nothing, I am guessing most merchants will opt to put in the work to accept cash rather than shut down.
There are attacks where bad guys will disable a gas station's dish (by covering it with foil among other methods) and then rack up a bunch of gasoline sales with a stolen card. They've got generally got a limited window so they have to hit a bunch of local stations quickly, but meth users aren't known for high dollar scores.
If we needed to leave due to an emergency, some cash may help for a hotel, probably, assuming it's far enough away to have power/water.
If there's earthquake/hurricane/etc with resulting power outages, most of the places I'd go to wouldn't be able to even open their POS systems to take cash in the first place.