Matt Lakeman's recent "Notes on Afghanistan" actually covers this as he first-hand experienced a similar situation in Afghanistan where the Taliban had shut off the internet:

"The internet was out. Everywhere. Across the entire country. No cell data, no wifi, no phone service, and as far as I could tell, there are no landlines in Afghanistan [...] But now the blackout was total. Our waiter was complaining to my guide that he couldn’t contact his mother in a western province. I saw other people in the crowded restaurant fiddling with their phones and looking annoyed. I asked my guide what he thought was going on. He shrugged."

"Without internet and phones, people can’t talk to loved ones, businesses can’t function, trade can’t function, and even government offices can’t function. Only the Taliban with their well-established network of short-wave radios can function. But still, if the internet remains off long enough in Afghanistan, the country’s economy and society may very well collapse. Afghans couldn’t get money from banks. Soon enough, would food stop being delivered to cities?"

https://mattlakeman.org/2026/01/05/notes-on-afghanistan/#

Russia has been systematically shutting down the Internet for a long time now, to disrupt Ukrainian drones. The effects were very painful intially, especially re payment systems; people were encouraged to withdraw and carry cash. Now they are shifting more and more towards a "whitelisting" approach where a handful of services continue to function while everything else is turned off. As usual in Russia, people complain but adapt.

Ironically, their long history of shutoff and censorship probably mean they're more resilient to stuff like this.

In recent years they have been trying to build a nation-wide Intranet that can function while international gateways are blocked. It is not perfect and every time they block the Internet, many issues happen but for the most port critical network services (such as payments) continue to function.