I do think altcoins disappearing will be a net positive for bitcoin in the long term. I think that it will make people realize that 99% of projects are just purely fluff, and what mostly matters is bitcoin. People are just creating blockchains for literally anything that it's beyond stupid. Think about all those scams that left a bad taste on people's mouths.
The market is big, people are looking to diversify their investment and I don't see any reason why altcoins should be eliminated when they offer great idea and they are building it for us to use in the future.
Diversifying your portfolio by investing in altcoins is still one of the most stupidest things that surprisingly, I'm still seeing in 2020.