bitcoin wont "replace" fiat.

fiat will exist due to minimum wage, legal tender, taxation, fines and duties laws. keeping fiat in circulation.
bitcoin will become a popular alternative.
but dont think bitcoin will become the only 'one world' currency to pay for every countries public services and civil servants/bureaucrats excessive salary.

bitcoin will be an open choice. not the only choice.

however while fiat hyper inflates (unrelated to bitcoin specifically but due to failings of fiat itself) yes people will realise hoarding assets its better. whether its bitcoin or collectable precious metals/gemstones