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.
Nothing will happen to bank. Some people are thinking that bitcoin will disappear bitcoin but according to me it is not possible to disappear bank because with out bank system countries are unable to do business with other countries yes I was agree with that bitcoin will reduce users of banks.