I think that only 10% coins/tokens that would be able to survive and will be worth investing in 2021.
There are currently 2400 tokens that are known and many unknown to anyone. By the end of the year 2020, at least 100-200 new tokens will be created. Every day in the world there are 5 new airdrops. I think it is not realistic to calculate. But I'm pretty sure new tokens are being created more than they are being deleted.
But we have to buy only good market capitalization coins. Don't invest money in shit coins.
As you said there will be more to come so we can't say how many will last, but we believe that the top cryptos will still be among the ones that will survive for me, that's obvious, unless there's going to be a big problem which will destroy them completely. There are already so many shitcoins and many more to come and we can hope that some of the cryptocurrencies that have value today may become worthless tomorrow.