He isn't. He most likely resides within the Composer's Abyss, waiting to unleash himself upon the defeat of Cortana.Yeah but the whole point is that he wasn't in Halo 5. The sole reason "The Next 72 Hours" was written was because they decided to go the Cortana route in Halo 5 and had to write him out if the story so that people wouldn't ask in Halo 5 where the main villain went.
But Reed didn't need to write 72 hours at all. We saw the Didact fall into a pit. As comic book villain deaths go its pretty workable end and ambiguous enough that you could bring him back whenever you want. He was already written out of the story.
Also, how can they possibly bring him back now? Nobody will have read that comic. You'd have to explain that Chief confronted the Didact and Composed him. This creates a huge disconnect between the events witnessed by the 99% and the 1%. Buts its an unnecessary divide. Basically they could have easily not written 72 hours and been in the exact same situation with the villain out of the loop following our heroes victory. They would have only done this if either A) It was important enough that those events happened B) They just wanted to sell comics.
Its more likely given the above that 72 hours actually comprises material that was meant to be included in the first act of Halo 5. But, this conflict was ultimately cut because it takes too long to get to the "Hunt" between Locke and Chief. The Didacts return in mortal form wasn't deemed important versus Cortana coming back; although potentially his later return as a composed entity himself might have much greater weight. Or, comic sales, I don't know and I don't particularly care; he was never a compelling villain.
Source? Have you spoken to somebody on the Dev team? Its your word versus theirs and people are extremely biased on this subject. I can certainly believe they made Halo 4 to be emotionally manipulative and seemingly kill off the character to bring her back. I mean I can remember a lot of speculation in the run up to Halo 5 that Cortana would come back.