In most Norwegian supermarkets the card readers (chip and pin and contactless) still work even if disconnected from the network. In my local one they just print two copies of the receipt and ask you to sign one just in case the reconciliation process fails when the network comes online again. Some small stores have an account with Vipps so if their readers actually are down but the phone network is up then they just ask you to pay with Vipps (https://www.lifeinnorway.net/what-is-vipps/).