ybrotes_Sargon
Restricted
Nihilus can be killed by anyone who succeeds him, has knowledge of who he is, and can cloak themselves in the Force {i.e. Dooku or Sidious}. Traya can be killed by anyone who succeeds her, knows who she is, and can shield themselves from a Force drain {i.e. Vader and, possibly, Revan}. Vitiate can be killed by anyone who doesn't underestimate him or afford him prep-time, which would most likely be Sidious.
Afterwards, Sidious and {possibly} Krayt are the clear heavy hitters on the field. Vader and Tyranus, each hating Sidious, will exploit the opportunity to kill him. Bane will probably join in as a master opportunist and Maul dies defending Sidious, or Bane will pursue Krayt and that fight may end in a victory for Bane {particularly should Bane be wearing orbalisks}. Tyranus and Vader, should they survive, will probably turn on each other. Revan and Malak, two impossibly inept tacticians, will {attempt to} destroy everyone in sight.
Sion will probably be pimpsmacked by any one of the above, but since all of the intelligent people are dead, no one will be able to manipulate him into killing himself and he will emerge victorious.