I’m sure by now savathun has sent at least some probes to the dreadnought to learn it secrets or sent larger forces to use it as another base of operations. The taken on the dreadnaught-if they were taken by oryx-are likely dead. Taken don’t have a very long lifespan, we don’t have exact timelines but especially if they were still on the dreadnought they probably wouldn’t last long. Hive-similar to the taken, the remaining hive of Oryx’s brood have likely died. They would have no leader and little purpose on the dreadnought. The sky burners would have also left if they had any forces left on the dreadnought to join the red legion.