[X] Kor'vas employs percussive maintenance to Kayn's head, as he must be broken if he's considering Gul'dan's words, especially with Illidan right there! Kor'vas' critical success cancels out Kayn's critical failure and both are treated as though they had a standard pass.
[X] Attempt to finish off Gul'dan and his forces without collapsing the center of the platform. Carries a bit of risk, but if successful would mean that you could be certain Gul'dan is finished off. Illidan would join in at this point.
[X] Drop the orc warlock into the abyss. Has a very good chance of succeeding, and a moderately high one of actually killing Gul'dan, but it is less certain, as he could pull off an escape, somehow. Illidan would join in at this point.
[X] Kor'vas shows what mercy one can to an Illidari who is fallen, and ends Kayn quickly. Kor'vas' critical success is used to kill Kayn outright. Prevents Kayn from joining Gul'dan's forces as an enemy.