This is a very difficult question to answer, particularly for someone who believes in bitcoin, I don't think banks will disappear as a whole but probably will change their system a bit, perhaps even enabling and using bitcoin accounts and paying interest in bitcoins.
The issue with banks disappearing is the fact they are the engine for finance, funding and financing everything from merchants loans to real estate, so, if banks disappear, what will cover these needs.

There are technical difficulties for that, increasing the block size seems simple and reasonable but that would require changing the whole bitcoin system to implement it in a wallet and would require every wallet/Blockchain etc... to have some change in it and that SHOULD be very difficult.