Bitcoin isn't going to make banks disappear. It's just meant to be an alternative payment/cash system. People will always need banks even if it's for just loans or whatnot. I suppose they could issue loans in bitcoin but banks will want to keep hold of the currency they can create/print/issue on their own will so in that respect bitcoin isn't preferable to them.
The central banks want to create or print the money. For the commencial banks, there is no difference between fiat and bitcoin.