Your just assuming that because we know 2 Didact will be in silentium that they both have to be in Halo 4. I wouldnt be surprised if Bornstellar died in silentium, which would make the ur-Didact the enemy and him hating John. And you really just contradicted yourself there. You said that it's unlikely that the Librarian would know to plant the Didacts into johns ancestors because the Didacts is in 2 entities. that's not true, he exists as himself and in a copy(Bornstellar), which would make it easier, because if I remember correctly, when someone has a Gaea created from them, they die, like lending your brain to the creation of an AI, so that assures us that one of the Didacts can be in halo 4. But then you said that out of "pre-destiny" John survived, which would completely make it possible for the Librarian to implant the Didacts imprints in John