Dude , let me make you understand that Bitcoin is not treated as a currency , but as an investment . And what according to you are banks. It's just a place to deposit or withdraw money and they will give you a certain interest on it. Bitcoin is a very bad currency , its prices fluctuate alot and people will obviously choose their countries currency over Bitcoin and so banks will always be in use no Matter what
money banks will be destroyed due to the more usage of bitcoins no more people will keep their money in banks thats why banks will be finished and then there will be the only kingdom of bitcoins on economy and than bitcoins will be known as king of economics.