It can be happen if eveyone all around the world start to using Bitcoin. For using Bitcoin wallet everyone should have a mobile phone. As we all know now a day mostly peoples have mobile phone and everyone start doing small to big transactions by Bitcoin. So it can be possible that Bitcoin can make banks disappear.
There will still be banks because not all people will adopt with bitcoin, the centralized system which are controlled by the government
will always be powerful but bitcoin is here to stay. Giving people different alternative is will satisfy them.