As Internet and email destroyed work of post offices about letters sending as Bitcoin will destroy banks system about using money. That is my opinion. And I'm pretty Shute that it is going to be as u say - bitcoin or maybe any other of crypto currency will be used mostly by people.
The banks are not used to send money. They provide borrowing and lending service. With bitcoin, they will make more money.
Yes, the job of banks are not only sending and receiving money for people, and also not only provide borrowing and lending service, but it has a vast field of work in financing of the state and for the organizations of the country.