Having finished Thursday War this morning, I think ONI's actions will need to come into play in future media. I mean, they killed off a lot of the Elites that are on the humans' side, to eliminate a threat that most likely exists only in their own minds. Should people like that be holding the Mantle of Responsibility? I don't think so. I couldn't help but be reminded of Joseph Stalin's treatment of his people. And since the Reclaimer trilogy is supposed to be about humans gaining the Mantle, I think ONI will need to be stopped, because if they have their way there probably won't be anything left in the galaxy but humans. And before you say "Well then, they'd be the dominant species, so they would still have the Mantle", remember that the Mantle is about protecting and watching over all life. Killing off other species and then claiming that you have the Mantle is like saying you're a responsible parent because you can look after yourself. In addition to their treatment of the Elites, I think their attempted execution of Halsey will need to play a role as well. Is Halsey really on Jul's side now? I say probably not; she's more likely "playing along" in order to get the other half of the Janus Key. But that's just my two cents. We'll need to wait for future media to be sure.
Now, the Arbiter. I suspect that the final book in the Kilo-Five trilogy will be looking at how he took being attacked by ONI, how his people are recovering from the attack by the Servants of Abiding Truth, and how Jul's followers became the main opposers of the Arbiter. I think at some poin't he'll probably catch on and realize that it wasn't Kig-Yar pirates that sabotaged his forces and take some kind of action, but hopefully not turn against all humans. Once again, that's just a speculation. We'll need to wait for the book (which based on the release dates of other books in the trilogy should come out this fall) to see.
And finally, the Didact. I fail to see how he died in Halo 4. He was wounded, but clearly not fatally, and then fell into the slipspace rupture beneath the Composer. Now, we know the Didact is immune to the effects of the Composer, but we don't know where he went when he fell through the rupture. The Halo 5 announcement trailer does seem to indicate that the Didact will be present in the game and the Forerunner machine featured looks like a War Sphinx, but it's kind of ambiguous evidence at this point. Oh well, once again, we'll need to wait and see.
What are your thoughts?