Banks would not disappear. Maybe the way banking works might become different, but even that is a remote possibility.
What you need to remember is that banking is big business. If bitcoin were to cause the banking industry problems, the banks would fight against bitcoin. And they would wage that war through government; By using legislation to keep bitcoin from causing problems to their industry. And government would happily play along.
Banks will not disappear but they are going to change, right now banks are researching and creating their very own blockchains, they love blockchain technology but hate bitcoin being on top of it.
I agree with you . could someday BANK will use the technology bitcoin in their financial system. to see these advantages, the BANK may attract more number of users more.