I'm sure someone will produce the quote where the devs said they'd never just relegate Sylvanas to go down in a raid fight. And no, "confrontation" doesn't necessarily mean killing blow (but She IS in the Gul'Dan spot as the minion in the X.1 raid, and Tyrande would make a wonderful Illidan figure in a clever "history rhymes" moment...), but that's not what this thread is directly meant to address, it's only an example of something that I've wanted to talk about for some time now.
I've been a D&D dungeon master for about 30 years. Not to toot my own horn but my players over the decades love me. In that time, I've said a lot of things in game to mislead players, and I've done a lot of intentional misdirection in those 30 years of storytelling. Some of it has been just accidental forgetfulness, some has been some Aes Sedai'ish word play of never committing exactly to one answer or another, and some has been a straight up demand for a straight answer out of me, where I feel I'm safe to lie to preserve surprise. All of these are fair storytelling tactics.
If the WoW devs tell us something objective about the function of the game itself, and they go back on it, they are fair game for ridicule and mistrust. Go get'em.
If they tell you "we'd never do that to Sylvanas" and creatively change their mind, that's actually totally fair and needs to be allowed. They have Q+A's, they take interviews. We get to corner them, and they are thus allowed to lie on story points, or even change their mind.
Now, that all said, they aren't entitled to your time or money either. I'm just saying that they are not required to be wholly honest when asked about the future of the story so far out of the moment. If they tell us "buy this expansion, it goes to the dragon isles," then have us go to the murloc isles instead, ok that's marketing done wrong. But we don't get to corner them into "you said you'd never ever do this" years before they come to the moment in the story and pull the trigger on what is, ultimately, a minor white lie of preserving surprise.
My opinion, such as it is.