Leak or not there are very few plot tracks left for D&D now.
1. Its very clear that the Great War will be and has to be between Living and Dead, there is no other twist possible...From the very first scene to the last episode, the great war has always been between living and dead, writers cannot change that to something else...Danny could have captured Kings landing in one battle, winning Iron throne is easy...
2. Jon is the most important Character to finish that war, he has been built up for 5/6 seasons for that, there cannot be a major twist in this regard. There will be one on one between him and Knight King at some point in season 8. It does not make sense Jon is killed off randomly or prematurely now, he is the main character, probably the reason for the show...
Why White Walkers became Active again and What they want?
White Walkers and Knight King has being living north of the wall for 4,000 years without much aggression. So why they are active again since the show began??
I think it has to do with Prophecy of Azora Hai, Knight Kings like three eye Raven(Bran) has ability to see the future. He knows about the prophecy and wants to change it. He wants to kill "Azora Hai", because he knows "Azora Hai" will kill him. WWs become active roughly around the same time when Jon was born, maybe he knew that "Azora Hai has born now, he wants to build Army and march towards south to go after him...
In the show we have seen quite a few times one on one interaction between Jon and Knight King, special looks both in Hardhome and last episode between Jon and Knight King, also validate some of this plot line...
Also, its very clear, Knight King is way more powerful than any other WW, even WWs are his slave (in a way), they all do what he commands. Whatever he (Knight Kings) define, is their mission...
Its sort of like Mosa and Pharon story, Pharon knew(via prophecy) one Israelite kid will kill him. He murdered every new born child to prevent that from happening...The life which Mosa leads was enabled by Pharon's action, he would have never end up living in the shadows of Pharon, if Pharon was not obsessed by the Prophecy... Similarly, Jon would not have led the life he has been leading if Knight King was not so aggressive in last few decades...In a way Knight King has made Jon, the Azora Hai, similar to how Pharon made Mosa