I'm referring to all cryptocurrencies being traded on the market today (Bitcoin and altcoins). As for Bitcoin, I doubt it'll ever go to zero because of its limited supply and widespread acceptance within the mainstream world. But altcoins can go to zero sometime in the future, if they're unable to deliver real use cases for everyday people. Most of the useless coins on the market with no active development or innovation will die, while very few will be able to retain their value on the crypto market. I believe that altcoins like Ethereum, Monero, Zcash, Dash, and even Litecoin will never go to zero as they're supported by their communities.
Couldn't agree more - the ones which are innovative and bring us development and interesting solutions will survive (but we should not regard them as investments, but tools used for some specific purposes, like staying anonymous, or providing instant international transfers of funds). Yet those which are nothing but a copycat, ripoffs will definitely not survive for a long time.