Not entirely true. The bitcoin exists, but cant be traded without power. Direct phone to phone transfer is possible and does not require a middle man like a bank. It is POSSIBLE that in a disaster where self electrical generation is possible (solar, diesel, genset, etc) that bitcoin might be the ONLY means of transaction due to the limited availability of cash.
The only problem is you can't verify the transaction in the blockchain. A full node wallet can do some verification but no phone wallets will have all those GB of blockchain data.
Another possibility is to transfer physical private keys sealed onto tokens under tamper proof stickers. You can't verify that the address on the token has been transacted the amount that the owner says was transacted. But you can look at the sticker and see it wasn't removed so the private key was not used and nothing was spent from that address. You also have to trust the vendor of the token. But you can get high denominations, as high as you want. I have physical with $5800 (at last check) that can theoretically be traded for something.