Or, Nihilus charges in and consumes the Sith Emperor. Checkmate.
Alright either Nihilus charges in and everyone gets consumed and dies. Or they all charge in without a doubt Malak dies in less than a minute. The emperor will probably use some kind of mind control on Sion as he seems like the most weak minded. Nihilus attacks Sion and they will probably get themselves both killed.
Revan and traya will be smart and sit back try to analyze and find a weakness they would last some time before getting destroyed. I see revan being the last one but eventually the emperor kills him or throws him in stasis.