Just for the moment, assume that re-incarnation exists. Especially, the soul of a dead person is only attached to a physical body the moment a child is born (not while in the mother's womb).
Then, which character do you think re-incarnated as Yang Guo? Do you think it Yang Guo is Yang Kang's reincarnation, or Wang Chongyang?
Why would Wang come back as Yang Guo? B/c he had unfinished business with Lin Chaoying. If you believe in the latter, that would make XLN Lin Chaoying's reincarnation...