I don't see any reason why ETH should die. It's basically too big to fail at this point. Even when there are coins that do everything better than ETH, Ethereum will still stick around.
Purely because it's widely accepted and well known.
Logically, if Ethereum dies, all tokens that are already dependent on the smart contract network will certainly experience the same thing. Of course it will never happen because of so much support from the community to the investors who are behind it all. And now that ethereum has made it to the price of $1200, who can stop ethereum? it's absolutely impossible.
Agree that Ethereum has got already strong position and it is a great doubt that Ethereum may die. It developed and is developing all the time. And as for Polkadot it is a good project, because it stimulates new projects to develop via platform Polkastart, because tokens of new projects are created mostly on ERC20. That is why Polkadot cannot make Ethereum to be dead, but just on the contrary.