ETH will die when another platform is better, and ERC-20 migration is as simple as a click of the button.
(this may be a long time away)

Of the altcoins, Litecoin and Bitcoin Cash will probably be the ones left.

Essential special use coins like Theta, and the upcoming SilverCoin (for miners and manufacturers) will survive.

And Dogecoin will probably make it because it will plug into everything.