Currently there are many new altcoins, there are hundreds or even thousands of altcoins. And not all of them are listed on Coinmarketcap. Altcoin which is registered in Coinmarketcap only and is ranked below there is a possibility will die because it does not have strong support from the public, especially altcoin-altcoin that is not registered. But for Altcoin which is ranked at the top, I don't think it should worry, because these altcoins are definitely able to survive.