I don’t know how Blizzard will play out the events following the story as it is. But I am one of those people that secretly suspect that Sylvanas Windrunner had everything to do with the assault on the Wrathgate which, in turn, led to the deaths of Putress and, more importantly, Varimathras.

I think Sylvanas had/has it all planned out. While she was probably more than certain that Arthas would survive the assault, she would succeed in a real life test of her plague against the Scourge and against the living. But, more importantly, she would be rid of Varimathras, whom she has likely not trusted since day one. Likely she was aware of some conspiratorial activities by Varimathras and allowed these activities to continue.

Allowing the attack on Undercity would suit her purposes and would give her credibility when she went before Thrall to present herself as completely uninvolved with Putress and Varimathras.

I am of the opinion that her vengeance goes far beyond Arthas at this point. I believe that she sees her people, the Forsaken, as her own personal Scourge army which she can use for total domination once her forces are powerful enough. But since they aren’t, separating from the Horde at this point would be suicide.

I am also fairly sure that her deceptive ways aren’t ignored by Vol’jin, Thrall, Cairne, or even Lor’themar (though Lor’themar would be the least likely to call her on it due to the weakened blood elf dependence on the Horde at this time). Given the troll superstitions about the undead in general, I’d say that Vol’jin would be the most wary and watchful of Sylvanas’ doings. You could argue, I suppose, that Lor’themar – who has the longer history with her as her former second-in-command in Silvermoon – might see the greater threat due to knowledge of her diligence and desire.

Sylvanas’ complete lack of emotion and concern for the humans or other living beings that she captures as test experiments (which is more than evident in the Arthas: Rise of the Lich King novel) makes her almost as bad – if not worse – than Arthas. Whereas Arthas’ path started with at least a desire to make things better at the moment of his turning down the dark path, Sylvanas has been driven by black revenge from the very beginning. Nothing good can come from that. She’s definitely more evil-aligned than Illidan Stormrage ever was.

The problem I am having is that, if she turns out to be a little evil and thus a killable boss at some point, who would lead the Forsaken after she is gone? The blood elves replaced Kael’thas Sunstrider with Lor’themar Theron pretty easily, but I don’t know who Blizzard could pop down to the Undercity to take control of the Forsaken. Assuming that, even after Arthas’ or Sylvanas’ demise, the undead state could not be cured (for game mechanic reasons), they would still need a leader.