Frosstbyte

Sylvannas has already been "killed" in Cataclysm. Or something. It's not entirely clear what happens to her, but this ensues in a cut scene type event during a quest chain in Silverpine Forest:

EDIT: I originally quoted a bunch of stuff, but it's easier to just link to the Know Your Lore article on Sylvannas from WoW Insider: Know Your Lore: Sylvanas Windrunner, part 2, page 2.

SF, if you want to interpret the game that way, I guess that's cool, but there's nothing any of us can say about it and no way for us to discuss it with you. The quests in the game say you're wrong. The books and comics say you're wrong. The cutscenes and old games all say you're wrong. We're not trying to dog on your interpretation so much as trying to explain to you that the stuff you're talking about isn't up for interpretation.

As someone else said, there's no way to interpret that Frodo isn't a hobbit. He is and that fact is crucial to his character in the Lord of the Rings. Similarly, there's no way to interpret Thrall's race. He is clearly and undeniably an orc and it is fundamental to his character that he is one. Important NPCs are often larger than PCs and less important NPCs to make them stand out and look cooler. That's the *only* reason he is larger than an orc in game.

So, as I said, if you want to "interpret" WoW in your own way, that's fine, but there's no way for anyone else to respond to it, because the story we're working with isn't yours. There ARE a lot of places of ambiguity in WoW lore if you want to learn it, but Thrall's origin story isn't one of them.