Curate, connect, and discover
So, obviously the rumors of Micah’s death is greatly exaggerated or misunderstood. We’re never shown exactly how he ‘died’ we just know he did and Angella feels responsible since it is implied it was her plan or decision that lead to his supposed death. Which is why Angella has a fear of making another bad decision that she didn’t make any decisions leading ( or contributing) to the original Princess Alliance to fall apart.
So, Micah isn’t dead. Then where is he? If he was a prisoner of the Horde he would’ve been used as a bargaining chip by them already. To get Angella and Castaspella to comply with whatever demands in order to ensure Micah’s safety. Both have a strong emotional and personal relationship with Micah, they would’ve done it. Two kingdoms submitting with little to no resistance at the same time would be a huge advantage for The Horde.
I theorize Shadow Weaver somehow has him under her own secret and private improsonment. Without Hordak’s or anyone else’s knowledge. Why would Shadow Weaver hide this from Hordak?
Simply because Shadow Weaver cares about her own magical power first and foremost. Even if giving Micah to Hordak would gain her approval and favor, Shadow Weaver has shown again and again, Hordak and his mission means nothing to her. Hordak is simply convenient for her goal.
The way she used Glimmer as a living magic battery while crude, but given the rushed circumstances she seemed to be comfortable and at ease with the situation. While showing disregard for Glimmer’s physical well being during this, it shows she has the knowledge to perform this and a lack of empathy to take magic from other’s regardless if it’s hurting them.
It also helps show that she’s hypothetically done it to Micah and possibly still did while she was in the Frightzone. Shadow Weaver probably has a complex spell or magical device that’s keeping him imprisoned (and out of sight) but alive enough to serve as a magic battery. Her being kicked out of the Frightzone has possibly cut her off from his magic.
Though, if he’s not being held by Shadow Weaver he’s possibly stuck or trapped in whatever area of the mission he ‘died’ in or he has amnesia as a result of the injuries he received on said mission.