The Stormheim opening cinematic starts with Genn opening fire upon the forsaken fleet. It is very clear, that Genn is the attacker and that Sylvanas did not know of him being there. She was prepared for the worst, which is why the Forsaken had an entire amada of bats with them.
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But Evir can die, just as anybody else. They might call her goddess, but she is not a god. Just like Odyn, she is a titan construct. She would be able to provide Sylvanas Val'kyr, but the alliance could always just free her. Also, Sylvanas already have some Val'kyr and she was nothing like a lich queen in Cata or MoP.
I don't where you get this from
In the leveling zone in Silverpine forrest and in the opening event of Stormheim, all she is talking about is how the Val'kyr are keeping her people alive and nothing about how she afraid of death. You sure its not some non-canon stuff?
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Have yet to see where Sylvanas is talking about being super afriad of death, even to the point of sacrificing her own people. The silverpine forrest questline is nearly all about Sylvanas, while being ruthless, really caring about her people's future. It is also said very clearly, that the Val'kyr is the only way for her people to have future, now that Arthas is dead.
And the plaque, that Sylvanas uses on the skyfire is more like nitroglycerin then a disease. The forsaken apothecary have found many ways to make chemical explosives.