We can't know if banks will disappear or not, but what we know is it will make a huge impact on them once bitcoin becomes ore mainstream, and the only way they can deal with not ending up like kodak is by accepting bitcoin and offering ways to store it for those that dont want to store it themselves.
Mainstream? Bitcoin is a joke right now in a lot of aspects, marketcap, usage, a lot of people trying to scam each other using the coin... Well, the truth is bitcoin users are on a bubble, it will be hard af to become mainstream.