Hmm. When I worked in retail (probably like 2008 or so) when the network went down we could still take credit cards, we young folks just needed a couple minutes tutorial from the more experienced cashiers on how to do the imprint machine.
I don’t think the extra fraud was a major concern. The person would need to happen to be in the shop with their fake card for this very rare event.
"What if the network's down?" is a problem solved by buying things another time on the rare occasions it happens.
Which I would posit is slightly better planning then having cash on hand, since it means you've kept a reasonable stock of whatever basic necessities absolutely can't wait.