At this point, I think it's a little premature to predict just what cryptocurrency will do with regards to anything, and most particularly banks.

There is a lot of wealth and power associated with banks, so to think that will just go away thanks to technology and mass adoption is unlikely. While much of crypto is based on some sort of decentralized blockchain, there's nothing that says those behind the world banks couldn't create their own version where they're still in control.

If those behind the banks were to underestimate the growing power and momentum of cryptocurrency until it was too late, then I suppose there's a chance for crypto to destroy banks. The likelihood of that level of arrogance though, considering how long these people have held and maintained power, is low.

Cryptocurrency across the board will need to improve it's point of entry, make it possible for more people to get involved and do so not only on a decentralized blockchain, but via a decentralized access point (without an internet provider) and via as cheap a device as possible. Then, it will need to weather all hack attacks, and gain enough trust by the people in order for the mainstream to feel comfortable with it.