I'm assuming she moves out and that's that? Dying would be so random. Still, a bit useless to write her in if that was all she was gonna do.
The wedding scene is definitely from the drama. That party scene was definitely not (why would Sadia be greeting her saas like she was in the OST?) The wedding is scene is probably gonna reinforce the "you can't forget your first love" theme and the OST will play while the 4 look at each other all sad and we get flashbacks đ