Banks will never go anywhere, banks will never disappear, as banks are into its opeartions since ages and it enjoys huge market cap and people always need banks to transfer their bitcoin to their bank accounts.
I don't think that banks may disappear even bitcoin is on high demand. Still banks will operate at this times, but banks may operate or transact with bitcoins.
I dont think it is possible. It can only reduce the normal banks. Many people need the normal banks and that is very important.