The death of altcoins. Clickbait.
You may think that Bitcoin can do what other altcoins do will mark the end for altcoins and that at some point in the future, Bitcoin may end up eating the whole cryptocurrency market cap and absorb once again over 90% of it.
Bitcoin indeed has Lightning Network to help it with small transactions, and now some developers are building side chains. A side-chain is just another network that utilizes the same asset as Bitcoin because the native asset is equal one-to-one, and you use that asset to pay for transaction fees and to reward Bitcoin miners at the same time if your side-chain is merge mining and has that functionality.
There is RSKsmart which is Solidity compatible which in short means that it can run what Ethereum can run because both networks use the same programming language, and Liquid uses a new programming language as such developers must start from the beginning because the difference on which projects were written, and other altcoins that have some sort of peg with Bitcoin but don't utilize Bitcoin equivalents to pay for fees and use cases in the sidechain an example of this is Stacks.
And even when you can run second networks on top of Bitcoin and those sidechains do what altcoins do the underlying issues Bitcoin has in the first layer remind there which is transaction fees. More transactions may occur on those second-layer solutions but in the end, you will need to settle on layer one if you want to hold the real Bitcoin BTC, and that is where the bottleneck will always happen.
Lighting Network is trying to solve the issue of small transactions in terms of value and the transaction fee that Bitcoin requires to remind decentralized, but many users don't desire to open their channels not just because there is a knowledge gap to entry, but also because you need to lockup prefunded channels or you need to have money and spend that money to receive funds. Some node operators are offering prefunded channel services or incoming liquidity but they do so for a fee and also since you are already in their hands using their nodes they can charge you a higher routing fee.
In general Lightning Network ends up being another fee market just like in layer. And those who don't know to run a node, nor have enough money to pay for incoming channels may end up just using custodian which in turn it affects the security of all users of the network because it centralizes the network into hubs and because it opens the door to issues like custodians miss using users funds or outright stealing them.
Sidechains may offer more transactions for the same fee or even lower fees but eventually, that same sidechain will reach its limit because they all work the same and store data in the blockchain, and soon enough that sidechain will end up needing yet another Lightning Network solution on top of the sidechain or something similar to process all the transactions users may bring.
If altcoins are already other networks and they are already running their data you wouldn't need a sidechain, and you wouldn't need networks on top of networks if Bitcoin was allowed to grow on layer one and just increase the block capacity as technology advances not just on hardware for the regular household but business too. That is why Bitcoin BCH is a thing because you can do all the peer-to-peer transactions on layer one, and any other sidechain on top of it will not suffer the bottleneck of small blocks, so I would say altcoins in general are here to stay, and Bitcoin Cash is here to be an eye soar and a reminder that Bitcoin can scale on-chain and in layer one.