You seem to assume that you're in a situation where, by assumption, cash fails but the whole computer and phone network infrastructure "just works". That seems unlikely. "Cash" is on your phone these days. I haven't spent a physical dollar bill in weeks.
SWIFT (Society for Worldwide Interbank Financial Telecommunication) moves a trillion dollars a week. I can't see the distributed blockchain handling that many transactions.
Unfortunately, the article does not talk about the GAS prices to make a transaction. For an average purchase of milk or bread the transaction cost will be too high to make crypto a feasible option for daily purchases during a war.