If botcoin really replace paper money, bank will be useless, we don't to use bank anymore if its happen. Government wil always protect their national currency so probably it wil not happen.
It seems to be difficult to replace the banks, if the use of bitcoin is massive and beat fiat then banks will accept bitcoin as a type of savings or commodities such as mutual funds.
Bitcoin will never be able to disappear bank because every country need bank system and without bank system no country can exist. We can accept this that bitcoin will reduce the customer of bank.