So Lich King will just take her back.If Arthas kiled her once he will do so again(not literal).
Orcs were idiots... end of story.
Medive was unlucky
Arthas had a choise but he made wrong one.
As i said before Lich King rules dead and dead are his and no free will is going to change that.
No, they regained there free will, he only had control because the fact that he raised them from the dead and had control, full control. That control was taken away from a lot of undead, thus, most regained there free will, like sylvannas, Lich King CAN'T just take control of it again.
BTW Orcs weren't "idiots" They had no idea, they didn't know what they were doing was wrong. Lack if information, and they weren't very intelligent compared to humans. Medivh Unlucky? Not really, not really the case.