Oh okay, I understand what you mean. I alluded to this in my write up, but it seems like they teetered the balance between closure and set up a bit closer to closure I agree, but the epilogue and the notion thatWhat Stalker just said. It doesn't look like there will be a natural progression into the next two games, it also doesn't seem like anything in the story has been set up for the long term.
the Didact is still alive because he slipped into a subspace portal instead of to his demise
returning to Earth and Halsey, going to other Halos the UNSC is stationed on (as you are the Reclaimer after all), getting a new AI, etc.
I think 343s plan is to use Spartan Ops, which occurs after the game is over I believe, to bridge Halo 4 and Halo 5.