I won't be convinced of his death until I see a body, but I know that's not necessarily GRRM's way. He is very clever, and I believe he wants us to think that Jojen was sacrificed. His mood from the earlier in the chapter and his later absence from it, Bran's fear, all the references about how "the moon was a crescent, thin and sharp as the blade of a knife." The description of the moon could just be a very curious way of conveying the passage of time (several months) or the fact that the action in the latter half of the chapter occurs on the same day. Notice that GRRM didn't call that chapter "The Sacrifice" (he reserves that for one about Asha) -- that would have been too obvious anyway, if Jojen was indeed killed, or simply false if he wasn't. GRRM's just giving himself some wiggle room and planting the seed of doubt in our heads. Jojen tells Meera that Bran isn't the one who needs be afraid. As Chrisdaw points out above, Jojen knows when he dies, and presumedly how. If you knew the moment of your death, would you be afraid when the time came, if you had years to come to terms and be at peace with that knowledge, as Jojen has had? No, I think if he is afraid, it's for some other reason. And as lostcause asks above, why would they kill him? Aren't there any Children with greensight anymore? Why would BR allow it, when he was the one who woke up Jojen's greensight in the first place? That's what we would call an 'Indian giver' -- giving a gift and then taking it away. Granted, we don't know exactly what's going through BR's wooden head, but I find it difficult to believe he would be so cruel as to grant him the ability to foresee his death that would be in fact be caused by BR himself. Jojen tells Bran "My task was to get you here. My part in this is done." He says "My part in this is done." That suggests he has more to do, just not perhaps with Bran. "He wants to go home," Meera tells Bran. "He will not even try and fight his fate." This suggests that maybe he's going to die there and not underground with the Children. If he knows his fate has something to do with Greywater Watch, then he knows that he's not going to die anywhere else. Now, it's entirely possible that he did give up some of his blood for Bran, if what Bran sees in the paste really is blood and not something that just looks like blood, as others have pointed out. But why, if BR tells him that Bran's blood makes him a greenseer, which is more powerful than someone who only has greendreams, would he need Jojen's blood anyway? BR tells him the paste "will wed you to the trees," that "the trees will teach you. The trees remember." Jojen doesn't have any particular connection to trees that I'm aware of. It makes more sense that there actually is weirwood sap in the paste as Bran supposes. He's eaten something that came from the trees, and that by ingesting it, can access their memories. That's all there is to it.