In re Lupin and Tonks: JKR said in a recent interview that Arthur Weasley was originally supposed to die in OotP, but she couldn't make herself do it. Nevertheless, she wanted somebody's dad to die in order to be a thematic parallel to Harry's loss of his parents. Therefore, I conclude that the entire Lupin/Tonks relationship was pastede on yey, in order for her to satisfy a thematic itch by knocking them off at a dramatic juncture.