I don't think cryptocurrencies will disappear. Cryptocurrencies allow you to make very cheap and fast payments between users. This is a real benefit that is in demand. Bitcoin and major cryptocurrencies will not disappear
For me cryptocurrency will not be disappear because as of now many cryptos are really trusted by many people and there are so many good benefits we are getting on cryptocurrency, that's why i am confident that crypto will be more popular in the future.
But there are a lot of people that don't trust it or even use or know it.
People are saying that cryptocurrencies will disappear not because they do not want it but because they know it will not be that used in the future and also because the government do not want it. It is decentralized and in the future, currencies might be digital than of a fiat. With that, there is no way to use Bitcoin. Might be still an investment but I think it barely survives at that time.