Originally Posted by
Beerbill Society
Exactly what Arthas and Kel'thuzad succeed in doing in Reign of Chaos.
Demons (Legion) were behind both of those forces so I'm assuming they wouldn't side with any of those in this specific event.
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They could try to pull it out, the ritual Illidan used something from the Tomb of Sargeras with the guidance of Gul'dan's Skull to perform that ritual, so it's completely possible.
What makes me wonder if Malfurion would try to stop them, I mean simply destroying the Frozen Throne has devastating consequences to Azeroth.
My point is Scourge has way to much plot armor to lose, if they destroy the Frozen Throne, Azeroth is doom and the Scourge will run rampart and destroy everything, if they managed to kill the Lich King the same thing.
Moving a War Campaign across Azeroth to Northrend and replacing the Lich King looks like the only possible way to victory, and even so, I doubt they could pull it out like both the Horde and Alliance of our time, with basically everybody else and with the power of friendship did.
Bear in mind that I'm considering Scourge at its peak, including Sylvanas, the Forsaken, the Fallen Kingdom of Lordaeron, the Nerubian and the troops that possible never died in Archimond attempt to destroy Nordrassil.
Even the full might of the Horde that came across the Dark Portal couldn't handle it alone.
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Now if you added together with the old Horde and Garrosh's Iron Horde I think the could pull it out.
Garrosh was a very successful at his war campaign against the Scourge, he basically was a front man against the Lich King in Icecrown Citadel and had the knowledge of modern weaponry that could hugely benefit the Horde war tactics to handle the massive amount of Undead.
They would still need the demonroids to win but it would be a fair victory.