No bitcoin can't make banks dissapear. Physical banks can dissapear, yes that's true but bitcoin won't be the reason that this will happen.
You're still going to need fiat if you're country hasn't adapted to bitcoin yet, so you will always need to exchange.
Yeah, bitcoin will be more powerful in future, but it cannot make banks disappear, as the majority of the population is dependent of banks and they would never choose bitcoins over the banks.
Yes, you are right but this issue is even more complicate.
The power of national currencies depends on many factors including the strength of the economy, national exports, services etc.
Bitcoin is not the local currency but global virtual currency and can't be easily linked to national economies.
Countries borrow money from national and international banks and repay loans in these currencies and companies depend on banks to.
Since bitcoin is decentralized and don't have central bank, it's not possible that bitcoin ever replace banks.
Bitcoin will remain alternative currency.