I'm also thinking about that, that banks will try to adopt the use of bitcoin and will encourage their bank depositors to use bitcoin as well. But still
banks can't be disappeared since they have a very important role in the economy.
Indeed they are way too big compared with other currency's, the fact is that banks will never disappear people will also always be needed.
Since the beginning of economy's time, in the history. There is already a bank, and I don't think bitcoin will make it disappear.
As a government needs a bank to be trusted for their financial system.