In a what-if scenario, Malak is redeemed rather than killed. For this debate assume his Light-side incarnation is as strong as his SF amp'd self. Revan and Vitiate are the same power level as they are in the book.
__________________ "Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."
Probably team if it takes Vitiate the same amount of time to take the fight seriously as it did in the novel. If he skips trying to TP them, I see him winning
It's honestly important to distinguish what is meant by "novel". I think Vitiate's approach on enemies in combat would be much different than how he moved against Revan. He remained overconfident by the end of the novel, but was more cautious overall and had already suffered a setback from one TP attempt in combat so would logically try a different approach next time he fights someone.
So, if we mean end of the novel Vitiate by novel Vitiate, then he is not messing around like he did against Revan.
Honestly unsure if Malak can contribute much here. He might be able to serve as a distraction, but even that could be pivotal enough to give Revan the win.
He lost to a weaker Revan despite having one of the most one-sided circumstances in the mythos ever. As I said, the biggest thing he can do to help is distract Vitiate.
And to be honest, the part about Scourge and the Exile changing the tide of battle was pretty stupid. Why didn't Vitiate just vaporize them?