Where are the real aliens in Oblivion? Surely with the TET destroyed they'll be coming back. Are they on Titan?
You seem to have missed an integral part of the story. There never were any aliens at all, only the TET. The message from Titan was from the TET alone, a completely artificial entity. The TET then attacked and devastated earth in order to drain its resources. The whole story about an alien attack that is told to Jack and Victoria (and all the others) was just a staging to keep him maintaining the drones and stay away from the remaining human resistance, which he thought to be the alien scavengers.