Well, if we compare it with the bank market in the USA. The world is still a lot of banks that do not have the strength of large, many small countries that need to be taken into account. That is the reason bitcoin would be more successful in many countries where people still do not have access to traditional bank. When people will have all the features of banking with bitcoin ecosystem then there is no need of fiat currencies and banks. I believe strongly bitcoin replace bank... It is highly possible that bitcoin is getting into mainstream adoption for all type of payments like both physically and online usage. At the time we do not need to convert bitcoin into fiat as all the services and  products will be available for bitcoin directly. So, there is no need of converting bitcoins into fiat. Then, there is no need of banking system.