Here's the current standings:
Loyalist:>Roboute Guilliman, Leman Russ, Lion El'Jonson, Jaghatai Khan, Corvus Corax, Vulkan, Rogal Dorn, Omegon
Chaos: >Magnus. Fulgrim. Mortarion. Perturabo, Angron. Lorgar
Chaos is outnumbered. If we add in Abaddon as another Primarch-tier character (come on he obviously will be), and Lion turns traitor, then the Imperium is suddenly outnumbered. The logical conclusion, then, is that Clone Fulgrim will even the scales and face down his original, slaying him for the Imperium.
THE EMPEROR WILLS IT!