@verglas there will always be someone who want to severe her life. Rememver when Lelouch made an effort just to meet her in person, in an utter to convince her to stop her campaign. At the same time, LELOUCH also has been planning means to pull Suzaku into his ranks. As a writer ofcourse we'd be however it is to be. The different of her when she was affected by geass and when she wasn't, was the very fact the she started the massacre and she openly did it like an idiot, which was due to his power being out of control. Even if all of them didnt get involved, Im sure L2 would try something. Or someone from Lelouch's ranks would mess it up. Either way, third party or not, it only takes a single death from "that" event and everything will fall into chaos again. Someone might frame Euphie, or Lelouch figuring out Suzaku's intimacy with Euphie and using it for his benefit. That event was the turning point when Euphie gathered the japanese people in thagt place so I think it would be nice to make it that "something else" happened there for the plan to deviate, ideally, a third party.