The Cabal are fighting the Vex, but running from the Hive. I wonder if it may be that following us pushing back Oryx (not killing him) the Cabal will move on to a plan to rid the solar system of the main hive threat by destroying Earth's moon.... thus probably decimating Earth too. I also wonder if by that point the Cabal will be split in some wanting to make peace with Earth to fight against the darkness (since the Guardians had power beyond theirs to push Oryx back ) and the main antagonists will be a splinter group of Cabal.