I highly doubt that we can leave banking on the side with just bitcoin. Remember, the point of banking, isn't just to store your money, most people do not even hold that much money in the bank idle.

Either you invest it, or you use it, you do not just put it in there idle doing nothing.

The amount of people who use loans, credit lines, savings accounts, basically things with that money, is the thing that keeps those banks going.

Even a very simple savings/loan bank, that just gets money from people and loan it out to others, uses the money. Bitcoin doesn't do that, you just either have it, or don't have it, that's it.