I was kind of expecting some dues ex machina or something to turn her into a wolf or him into a human or make her immortal or whatever. However, one of the things that I began to really enjoy about this series was the insistence that they would love each other while she was a human and he was a wolf, while she would die and he would live on. There were no sudden miracles but one that was plausible given the other events in the series (the cherry tree incidents, his and his son's own evolution from ordinary wolves to those that can call upon the power of the moon, etc). Allowing her to become absorbed into the cherry tree and gradually accumulate the power of the moon as he did was a nice resolution to their "forbidden love."