I think for now, all the Altcoins will likely survive 2021 unless something huge happens and set the space back like 2020 Covid 19 thing. In a bull market even shit of the shit coins pump like crazy, it is you that would be wise enough to know these projects can sustain their price and get out with profit
All those shit coins are those that will die off at the end of the bull because they hype and pump as fake projects. However , nobody can say this or that altcoins will disappear from the market but surely those between the top coins will still survive the heat if it starts.
But one way you can know a coin that won't make it is when the team are not working, if they have abandoned it and not creating new and purposeful innovation, they won't have investors. This will at a time pull down the project. So investing in top coins still the best .