I thought it was confirmed Evil Cortana was one of the rampant fragments that got blasted from Mantle's Approach.
Quote from 'Dominion Splinter': "Don't worry about me. I'm a fragment of what I once was. This splinter of me is no threat to you. Or to this place."
She makes contact with the Domain which is what allows the fragment to rebuild itself, but something built on a shaky base will topple.
I feel like this Halo game is going to be a lot more open ended in terms of gameplay. It will still be the FPS we know and love, but maybe have a lot bigger play areas on multiple maps and locale/planets. Maybe using Infinity as a home base you will have a galaxy map where you chose in which order to play them in/ where to go?
I hope it reunites a lot of the loose ends and side stories. Chief comes across Spirit of Fire. Gray Team is on the radio in one part. We see a Vulture shooting it out with some Banshees. All the side stuff in this one Infinite experience.
Probably be smart and don't trust the trailers this time people. 'Hunt The Truth'
They have never been game accurate so don't be angry when the aren't.