It doesn't matter. You don't need to destroy them, just win by getting one of the win conditions.

i assume Zongheng are the corals? I also had a game where I disabled all victory conditions except for domination and that game turned out impossible, as the corals just always force peace
if you want to have a domination victory you have to take out the coral empire very early, if you wait too long they can no longer be declared war against as their influence production becomes higher then the cost to force peace