The theory that the parents killed Madeleine and a friend helped them get rid of the body is no more far fetched than the one that Madeleine was abducted by someone who had watched her night after night so as to decide when to abduct her. but it is that, just a theory. I never said that I believed that was what had happened, just that that could have been what had happened.
I do not believe that Madeleine was abducted. But if she was, then I do not believe that she is still alive.
But I think it's far more likely that someone in that party had something to do with her disappearance. These things do happen, and just because a body hasn't been found doesn't mean that she is alive.