I don't think that bitcoin has the potential to make banks disappear or even make banks useless . the government especially those elites wouldn't want it to happen even if they already have the control in bitcoin .
Yes, banks is the economic and monetary lifeline of every country and it cant be replaced by BTC, plus how can we encash our BTC if the banks disappear.
Yup in this world we live in Cash is still king. Bitcoin without banks or even Fiat can't act on his own. Bitcoin will have no value on the majority of people who don't know it yet. Even in the near future I can't see Bitcoin overtaking any Fiat currency. Because in order for you to use Bitcoin you need to have internet and not all people have internet.
As bitcoin users and supporters as well we think of the better future of bitcoin, but let us consider the reality that it will never be bigger than fiat. We can use both to have a better like gaining from the benefits of using bitcoin, however we cannot deny that all people needs fiat as it's widely accepted compared to bitcoin.