In the far far future, because banks are very big organisations and its obvious that banks are putting a lot of effort to fight with growing bitcoin popularity.
I too believe that Bitcoins can disappear banks but not that fast. The banking system is trying hard to push back cryptocurrency. But this won't be happening. Banks can make bitcoins harder to access. I think eventually Banks wont be able to stand against bitcoins.
Seriously, what makes you think that Bitcoin stand a chance against mighty banks, and indirectly the governments as they support fiat banks?
Governments will never allow Bitcoin to come even close to damaging their in full control banking system.
If Bitcoin comes too close, then governments will force banks to adopt new rules and policies regarding Bitcoin usage, and maybe even a total ban for companies to do any kind of Bitcoin related business.
That's why I prefer Bitcoin to be and stay an alternative option to fiat currencies and banks as that will suit a lot Bitcoiners much better.