If you take Bitcoin as an example, then its quantity is limited. And accordingly, the demand for it will increase. This means that the price will rise. After all, since many Altcoins are similar to Bitcoin, we can conclude that cryptocurrencies will not go to zero.
Technically, Bitcoin prices should rise over time according to its limited supply. Unfortunately, that's not case today since people are focused on Bitcoin as a sort of "get rich quick" scheme than a real store of value. It's that sentiment which harms the value of Bitcoin and other cryptocurrencies in general. Considering that people are the ones who give value to crypto instead of a central authority (unlike Fiat), prices can go all the way to the moon or all the way down the drain in an instant. We all know that crypto still lacks real use cases for the mainstream world. On the other hand, national currencies (Fiat) are much more stable in price and transactions performed with them settle instantly (depends on the situation). Since they're backed by the full faith and credit of the government, people tend to trust them more than crypto itself.
If crypto fails because of its inability to provide real use cases for the mainstream world, then its price will go to zero across the market. It's all about providing usability in order to increase adoption of crypto than anything else. So far, Bitcoin has been able to survive as a censorship-resistant cryptocurrency for the world. It may not be useful as a currency for day-to-day transactions (yet), but it's a rock-solid store of value that's often comparable to Gold. I believe that in the future, only Bitcoin, Ethereum, and a select number of cryptocurrencies will retain their value across the market while the rest will simply go to zero. Aside from providing real use cases for the mainstream world, what gives a crypto's value is constant development and innovation. There are hundreds of coins out there which are simply copies from one another without real development at all. A cryptocurrency with active development and innovation, will be able to become more "useful" for our society.
Nonetheless, as long as the money is flowing into the crypto market, there should be nothing to worry about. I hope that worldwide governments and crypto would cooperate in order to keep the Blockchain industry alive for the foreseeable future. Only then, crypto will be able to retain its value across the market. Given how long crypto has been actively traded and supported by people in the mainstream world, it looks very unlikely it'll go to zero anytime soon. Just my thoughts