I think that the DA will play an important role in the new book, but I don't think Harry will be happy about it. I really don't think Harry feels he has to do this alone so that he can look better, I think he genuinely feels like he is the only one who can, and that he doesn't want his friends involved not because he wants all the glory for himself, so to speak, but becuase I doesn't want them to be hurt. Look at how he felt after Arthur was bit by the snake. He felt such extreme guilt becuase he saw it through the eyes of the snake. I do think that his friends and the DA will not let him do this alone, no matter how much he fights it.