In my experience, for the 4G/5G network to be down something really serious must be happening. I had long power outages (more than a few hours, in some cases even days) that affected multiple regions in places that I lived before that still had working cell network. I assume cell networks have backup power and preferential usage of the power grid, but I am not a specialist.

And I am not saying that you shouldn't accept money as backup, of course you should. But what I am saying is that you can still accept credit cards even during most power outages.

Same as Software Engineer, it is impossible to have perfect, 100% reliability, but it doesn't mean we can't improve from 99% to 99.9%, for example, to have a better service.

If a city has an extended power outage such that the battery backed cell network goes down, then everything else will be failing too and payments are the least of your problems.

Without electricity the water system depressurized, which contaminates it. After about a week the sewage pumping stations have backed up so the sewer system is starting to fail.

Modern cities cannot operate without electrical power given their scale and density.

It is bizarre to think the biggest problem is "how do we keep a transaction of value?"

Like, just declare an emergency and let business owners be reimbursed by the government.

Credit card processing existed before widespread telecommunications infrastructure. Maybe we should require payment cards to have raised numbers like they used to so the old carbon copy machines continue to work.

Credit cards and payment networks have always explicitly supported "Offline" processing like that.

The kind of fraud that system enables isn't really common.