I believe that Ethereum should not die abruptly. There is no reason for this. But it may gradually give up its positions - this is quite likely. It will be replaced by more technologically advanced, lightweight and convenient counterparts. It is competition that breeds progress.
You are right that Ethereum will not die all of a sudden but gradually when its Competitors will come up with better Technology at lower price. We are living in the age of Market Economy where competition breeds progress and development as a result consumers get better goods and service. There is more innovation as firms look for new products to sell it at lower price.