With all this talk about Fred, Linda, and Kelly making an in-game appearance, we seem to have forgotten that Gray Team (Jai, Adrianna, and Mike) is still out there somewhere. Where did they end up after the Human-Covenant War? I think their story could go a number of different ways; maybe meeting up with the Spirit of Fire, or being stranded on a Halo ring or shield world. Not impossible, considering they usually operate far from the UNSC.
I would love to see Gray Team get their own spinoff game rather than see them in a main Halo title. However, I agree, I would love to see them appear once more, be it in a game or in another novel. They’re far too interesting of a team to let their fate go unknown.