It should be mandatory for critical infrastructure like ATMs to have 24hr batteries installed. And some sort of power backup to maintain internet access as well - even if it's just a matter of everyone being allocated a small amount of starlink data or public wifi.
These things have relatively small costs, but make the system much more resilient.
My fear is that without access to cash, people might loot stores or riot to get essentials, once they get desperate. Keeping ATMs online for longer would make that kind of event less likely.
These things have relatively small costs, but make the system much more resilient.