Banks cannot disappear, it might be possible that physically banks may go obsolete, but electronically it will continue to function. Bitcoin is great but some features are missing which general people will like to have. And also the trust factor towards a bank is too high.
Banks are somewhat a foundation and institution already in the financial market and standing there for centuries already, it is somehow have some pride or just trust issues in giving in with bitcoins. Although, they will work hand in hand in the future.