I think you're all forgetting who Mara Sov is. She wouldn't be evil and turn on Earth. She merely looks after her subjects, which is why the Awoken are allied with the House of Jusgment; it was Variks' valuable history with Skolas that led to his capture by the Queen. I imagine she'd turn the Taken into another race to rule, much as the Awoken. No harm to Earth, just protection of the Reef.