Right now we haven't got more of the direct bitcoin acceptance. As stated soon we'll have the increased acceptance in stores as well on our needs. This will surely decrease the usage of banks, because now most of the bitcoin users convert the bitcoin to fiat just because they don't get the chance of using it around their locality.
One thing i have to defer here is that even if bitcoin is accepted world wide then there wont be any decrease in the usage of banks because you need both fiat currency and bank to invest in bitcoin or any alt coin,so they will co exist in the future and it will be like that in the future.I am not sure i am able to reply to what OP is trying to tell here. 
How the bank will be going well for example if bank. If there are a lot of money is coming to bank by people as the price increasing of bitcoin like that bank will giving loans to people and take a reserve rate to Central bank.