You should also think that not everyone can afford to own internet, pc. You also have to keep in mind that not everyone has the ability to learn technology today, because even with the simple use of mobile phones, many people still find it difficult. So in my opinion the fiat currency will still remain and will not be lost, it will continue to be available to us for a long time.
Bitcoin is not created to be the sole currency in the world but it can be used for global trade without converting your base currency to different currencies and if you look at bitcoin in that aspect then you will understand that bitcoin can be used parallel to the fiat currency. There are many third world countries where they cannot afford all the luxuries but majority have mobile connection and if we have more companies with good user friendly application then everyone can use.