Bitcoin being an E-curreny can't make bank dissappear; for one thing, here in our country Botswana, we get alot of power cuts, relying on online currency is a really bad thing. Its best to know that you have something physical to use even if the whole world goes internet dark.
This is a very important point.
Even in areas with reliable power, having everything based on a digital currency is very dangerous.
In the future, cyber warfare will become a greater threat. If an enemy is able to cut off power or internet, you would need to have some form of physical currency.
For this reason you probably always need some form of fiat in paper or coin.