For me It' very obvious she didn't leave on her own, because she was just unhappy with the group's direction or smth simple like that. It was really unplanned. Otherwise, they would probably discuss about she promoting with the girls until they finish the schedules in the end of the year, so the group wouldn't suffer any hit.
exactly, the way they didn't even bother with a so and so is on hiatus for x issues, which then later becomes a way of easing them out the group..