I don't think fiat will ever die as opposed to what other people are talking about. Cryptocurrencies are just an alternative for fiat as payment for online services and goodies and other stuffs. But it's a good case if we have a hybrid currencies where cryptos and fiat are at work all together.
To anticipate the digital technology that is certain to come, cryptocurrency is ready with blockchain technology that accommodates users in conducting trade transactions, making it easier and more efficient. Unlike transactions using fiat money uses a lot of costs, is longer and is not transparent. But both systems have advantages and disadvantages, so they complement each other. Because cryptocurrency remains an alternative payment tool, after fiat money.
I think it will be great if the fiat and crypto will work together because there possibility they help each other especially when it comes there value. And possible cryptocurrency will be more stronger while fiat will be easier to used. But the only problem is if fiat and crypto collaborate then surely huge changes will happen in both of them.