I believe that maybe, after news of how the cabal where unable to gain the acceptance of the traveler, the fallen will see that indeed the traveler does what it wants, even when an alien race has completely destroyed the last of another's kind and captured the traveler itself. Maybe, the fallen will see that violence and stealing the traveler back is not the answer, and maybe they can form an alliance. Throughout the lore even in destiny 1 it has shown that there is a strong possibility of a fallen/human alliance, and especially now, one of the mission straight up hints at this. "The enemy of my enemy", a mission where you save a fallen captain, and the fallen captain gifts you with a methane reactor core, capable of hooking up to a servitor generating mass amounts of either for his fallen. The old phrase goes as follows: "the enemy of my enemy is my friend." Finish the mission title, and you can see the meaning behind the mission. As the ghost said, throughout the mission there is something unique about this captain, how he seems smarter than the rest. The fallen are hard to understand.