Basically if you compare demand and the technological use of Ethereum it is certain that Ethereum will not come to and end.
And base on its support from the people, I doubt that ETH will come to that point.
Okay, let's say that ethereum is going to $50, so what? I bought at high price so that really means more ethereum if it goes low. This isn't only about the profit taking but the way on how you are going to accumulate more of it while its low.