Well, I don´t think Yuki´s going to kill Sara. I think she´ll be killed by Zero or Kaname.
*Random Theory *
1. Sara will get Zero. But I don´t think Zero will be beside her spontaneously. Zero wants to kill K, but he obeys the rules of associations. Then, Sara will have to control him.
2. I read on LJ that Sarah can control people when she touches them, because every time she wants to ask something to someone, she touches the person (Takuma, girls who were turned, the hunter). And we know that PB vampires can control others vampires.
3. Zero has a great sense of responsibility and that is why he's not hunting Kaname yet. He´ll do this if he´s authorized.
But ... Zero is falling. Then he will get closer of the LvlE condition each chapter. And this condition changes his mind. It´s very possible that his sense of responsibility will be overwhelmed by his instinct.
4. Sara is a PB. PB control other vampires. Zero is falling. There is a suspicion about Sara, maybe she can control who she touches. Sara is manipulating the blood tablets.
5. So it's obvious that she´ll do everything to get Zero in this context.
So I see it:
Sara will control Zero. They will fight against KanamexYuuki. Kaname will be hurt. But Yuki will prevent Zero to kill Kaname. She´ll use the bracellet . I think Sara is going to kill someone who is close to Zero or She´ll turn someone into a vampire. So, Yuki will take Zero of Sara´s control. And Zero´ll kill Sarah.
No, I don´t see Yuki killing Zero. He has asked her to do it and she said she can´t. But she promised that she´ll stop the monster inside him.
So, end = Yume and ZeroxMaria. Amen