I think Halo should split up in two Canpaigns:
The MC vs the dark new threat (probably the makers of the flood and their alies)
and
the Sangheili vs the Jiralhanae.
Finally both campaigns unite and the Sangheili regain their technology through Forerunner Help as well as they warn the Galaxy about the new threat.Humans,Jiralhanae,Sangheili,Unggoy,Yanme'e,Huragok,Forerunners,Mgalekgolo,the remaining San 'Shyuum and more species unite to face the dark extragalactic threat.HALO is ready a Chaotic sequel.