I don't think fiat will ever crash. At least not in our lifetime. There will always be a use for it, just like there will (now) always be a use for BTC/alts. We just don't know what those uses will be in the future, yet.
Until whenever the country will continue to protect fiat for being a symbol of the country, besides any sophisticated technology then the use of fiat will be used, a small example is we pay $ 5 for parking and of course use fiat because if using takes more than 15 minutes so it becomes a queue problem.