I don't think traditional currency will be replaced. Bitcoin and other cryptocurrency will be an option. Many of us see the future of bitcoin while other people do not even have the idea of what is crypto. It is not really safe so we have to be careful and learn first the security of accounts when using bitcoin.
I think the same and when I first started using Bitcoins, I used to consider it as an alternative for PerfectMoney and other payment processors which was easy to use and no reversible transactions were possible which was a big problem with using PayPal. I think Bitcoins as we call it - cryptocurrency so we better understand it as a currency only which works in tandem with our fiat and other payment processors.
Traditional currencies cannot fade away just because bitcoin started dominating the market in terms of price. No matter how valuable Bitcoin gets it will always be considered as an alternative but the primary and traditional payment methods will remain. Maybe the number of transactions happening over the crypto network increase and more people use them but again its just Bitcoins becoming more famous still not replacing fiat by any means.