Altcoins will never die, as developers launch new projects on a daily basis. Old coins will die (except ETH and a few others), while new ones will take the reigns as the "next big thing" in crypto. Bitcoin is the main trigger of the market, so if BTC prices go up, altcoins will do the same (or the opposite if BTC goes down). You have to consider that altcoins have a lot more risks than Bitcoin itself.
If you know how to play your cards right, then altcoins make the perfect "tool" to grow your investment in the short term. Otherwise, I'd suggest you invest only in Bitcoin to play it safe. The crypto market often comes with surprises, so who knows if you become the next crypto millionaire by holding prominent coins for quite some time? Just my opinion
Altcoins aren't a single coin so there is no way that all of them will die but many of them are now dead because they are weak and scam. Good altcoins can suffer from a bearish market but being dead isn't the best way to call or term them during these times. You can't call something dead if they are still active and can recover by the time the bull season came in, and also it was the new coins who has more chances of dying because new coins usually don't have anything new to offer as almost all the ideas are already given by the old coins. New coins are only good for the hypes so we can still invest on them for short-term gains. If you know how to play your cards right, then altcoins make the perfect "tool" to grow your investment in the short term. Otherwise, I'd suggest you invest only in Bitcoin to play it safe. The crypto market often comes with surprises, so who knows if you become the next crypto millionaire by holding prominent coins for quite some time? Just my opinion