I have seen people say a lot of things and the opposite end up happening, I am not totally ruling against that possibility but you should also be aware that nobody can predict the market correctly, it is possible eth will dump as they claim or even pump unexpectedly. it is up to you to make this tough decision.
Assuming it is 100% certain it will dump, selling now will be a good choice to be able to buy more than what you previously own but who knows what will happen.