I could see Tyrande do this if Malfurion actually died, because the entire conflict would become far more personal for her then. But he did not. Although I'm not sure the Blood Elves would be the target of any of their rage/anger right now, since they seem to keep out of the conflict so far.
And of course, payback is sacking undercity.
Honestly I'm more concerned about a different story than fictional morality. Cause one way we end up with MoP2 and the other we actually get a new take. And I'm not gonna lie, I want the Night Elves -at least a group of them- to snap after this, to have REAL consequences for the atrocity beyond the alliance races taking the high road. Not only because it's a different narrative, but because it also speaks more truly about the reality of war, and how a huge atrocity can lead the "good guys" to commit their own moral mistakes.
Although the idea of Alleria being as much as a race traitor as Dar'khan while screaming "See Silvermoon is Alliance now!" to a field of blood elf corpses is pretty hilarious, bonus if she screams about not understanding why the Sin'dorei don't like her.
My goddess? have you abandoned me?
Now you are thinking like blizzard! Better yet, make the fire out of wisps so it is magical fire and it has story resonance lol. And it works.Or even worse, having the night elves camp outside the shield because they couldn't get in, so they try and use torches to burn the magic shield down.
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Now that would be morally grey. Or she forcibly converts them to the void and the Sylvanas similarities go completely unnoticed.
Although using Tyrande and Malfurion to showcase the inner divide of the Kaldorei (Retribution versus Forgiveness) would be actually kinda cool. Their failing marriage the representation of kaldorei society's division after the Burning of Teldrassil.
"Tyrande, no... I cannot follow you down this path."
"I know, I know you my love... I can live without you by my side, Malfurion, I did for thousands of years. But I cannot live without Justice for our people. Like you."