I think banks will still stay for a long time because that not everyone still seems to trust bitcoin and not everyone has the knowledge to use it like my parents they know about bitcoin but they still want their old trusted banks i think maybe after a couple of generations in to bitcoin the banks will disappear.
I also believe that banks will not disappear because of bitcoin though many services of banks can be elliminated because of bitcoin. Banks have services that bitcoin alone cannot accomodate like loaning and saving interest rate. Many people will say that they will earn more on bitcoin rather than on bank interest but the question is does bitcoin is fully accepted in your country I mean even local stores accept it?, if the answer is no then bank services is still good for local transactions.
This is why I think fiat can live along with bitcoin as some sort of competing forces to maintain a continuum of inflation vs deflation. I think it's clear that bitcoin can't deliver everything that fiat currencies can nowaday, but who knows if in the future, my means of sidechains, we can get loans and saving interest rates that is based on the main BTC chain, kind of like gold 2.0 and then actually verifiable fiat based on this gold 2.0 of 21 million bitcoins? That is something to explore in the future.