If cryptocurrencies will be the basic mode of exchange in the future, what will happen to the banks then?
You can not worry about banks. They worked and will work even when the crypto currency partially displaces fiat, and will also become the main form of financial settlements between citizens. Banks will in any case find a job and will continue to extract their profits, perhaps not so much. Banks are needed by the state and the state will always support them. Implementation of the country's budget has always been and will continue through banks. The main income of banks - the issuance of loans will also work in any situation. Crypto currency can not perform this function due to its nature and high volatility.