I don't think BTC or ETH will perish anytime soon. For BTC, it is on the path of becoming too big to fail, with the billions of institutional investment money pouring into it. Those investors have the holding power, and will not run out at the drop of a hat when the market moves. That gives BTC the intrinsic value, and makes it different from the meme coins that can drop in half or even more overnight.

As for ETH, it is still around and growing now, with more and more applications built on the network and more values locked. Once it finishes the transition to POS and sharding is in place, it will be able to fly at full force. It will be interesting to see what happens to all the layer 2 solutions on Ethereum with that happens. As for the other layer 1 platforms, I believe some will disappear and some will still stay, depending on the values that they can offer to whoever stay on their networks. There are multiple telcos serving the same country, so it's possible to have multiple layer 1 blockchains as well.