Always it is impossible to predict the future of altcoins, but at the same time block chain they were designed for continue to be used and developed, then the altcoins will continue in future also. Altcoins have a smaller investment when compared to Bitcoin. Many governments around the world are beginning to be legal to cryptocurrencies.
As long as bitcoin keeps doing halving mechanism and the chance for altcoin to increase will always there. The main important thing is since the inflation of bitcoin will have decreased due to the bitcoin halving and it will be also pushing the price to go up as soon as possible after halving has been happening. The futre of crypto will be surpassing gold. it will be achieved soon.
In my opinion, there is no guarantee that after the Bitcoin halving, the price will always go up, it's been 2 halvings, the price of Bitcoin has always increased and reached new ATH,
but at the next halving it may not happen, even the current altcoins, in my opinion, will be difficult to rise , only a few who do have good fundamentals will follow the bull run, so if you believe in altcoins,
my advice is to invest in altcoins that do have good fundamentals.