In the story trailer released today you can see footage showing Nathanos in a battle with presumably Tyrande. He is smashed against a wall and pinned down on it with a silver arrow. The camera then shows Tyrande.
So our fight against him in pre-patch was maybe part of the plan so he would get killed and able to join Sylvanas in Shadowlands? Anyway he gets smashed around and Tyrande gets her revenge it seems.