Originally Posted by
Maxilian
Well they did, but not cause they were powerful enough to do so, but because Illidan pulled a Nerzhul, the Illidari worked as a distraction (a really good and powerful one)
Note: In the end, i do think that the Scourge would end up winning, even though the Illidari are quite strong, many of its forces are also going to eventually become reinforcement for the Scourge, and the Illidari doesn't have any powerful weapon against the Scourge (as their main power is against demons not undeads, so that doesn't give that much of an advantage, while the magic of "death" is quite effective against the Illidari forces)
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Is not the only weakness, but the death magic can (depending how powerful the spell is) evade the demon soul to even going back to the nether to reform, though i don't think is that relevant as most forces of the illidari are living creatures (so the scourge can use them after they slay them)