I believe that is it absolutely impossible that btc will destroy the bank system.
Beside its unpredictability, how could btc ever reach every country in the world? Think about the third world and remember: no internet no bitcoin.
I think that it is also impossible, for fiat still rule the world, and of course the fiat will continue to live because it is assisted by the government, so it is impossible that the bitcoin could make bank disappear
This is the reality that we can't change, fiat will still the most used type of currency and medium for different transactions. Even though there are online transactions or being paid by credit cards, still people will convert it to fiat and the banks are the ones who are responsible for doing that. So, bitcoin profits that needed to be sold and converted to cash, banks are needed for it so they will not be gone, they will remain.
That's true, we will not exist without banks, bitcoin is just a small part of a currency but it has not gain the trust of the majority, bank does. We have to be realistic and admit to ourselves that it will not happen that bitcoin will make Banks disappear. Instead we have to appreciate that bank and bitcoin gives us some comfort for our transaction having two options.