I'm pretty sure that the "Light" we have as guardians was given to us by the Traveler as a last line of defense because Rasputin prevented it from leaving. It's in a "dormant" stage now because all of it's light is in us/ghosts. I personally believe that the Traveler will take it back as soon as it can flee. I also like your assumption and I believe that you may be right, but I also think that the Fallen never saw it coming when the Traveler left, so they couldn't make preparations. Dead Orbit could be stockpiling all of the histories and discoveries and great works of man, however, because they have it all planned out that they will be leaving their home to make a new one! Just a thought, with plenty of speculation of course!