I'd say that it'll probably be used to jolt him out of the mind control at some point. I seriously doubt that they'll kill off Anduin or make him remain MC'd or w/e by the end of the expansion.
EDIT: Besides, his experience being mind controlled and then breaking free will probably result in some key speech about how "Sylvanas' actions weren't really her own and if Anduin's actions can be forgiven, then she should be forgiven too, and yada yada yada." Basically a repeat of the whole Saurfang/Anduin "The Alliance has blood on its hands too" conversation. I'm 100% sure that it will go over well.