I believe that it will have an impact to the fiat currencies, but not to the value of the currencies. BTC and fiat currencies will adapt to each other and certain alterations will be made in order for both systems to work together. I don't think that it will replace fiat currencies or devalue them, but they will all be present and active in the standard banking system some day. The banking system will have to adjust and alter in order to implement cryptos into its system.