Happy stories are rarely ever happy if you look past 'The End'. Harry Potter marries Ginny and gets a job fighting dark wizards because it is expected of him and he is so tired of fighting. He has two sons and stops looking for little blond girls that frequent astronomy towers. Luna Lovegood spends her time trapezing obscure forests in search of creatures she knows do not exist. She dates a magizoologist who can at least pretend to understand her, and the monster she holds never quite learns to live without a vice. She does not drink, and she avoids boys with dark hair and too wide smiles.
When they meet again at a DA reunion, they do not do not slink away to a dark corner to cheat on their significant others, nor do they share one last glass in remembrance. They acknowledge each other as old friends, no more.
Four months later, Harry Potter is killed while on a hostage rescue mission. Before dying, he managed to save four wizards, including a little girl with blond hair and silver eyes.
Just two weeks after that Luna Lovegood disappears while exploring a forest in Switzerland. Before her death, she sent a letter to her boyfriend Rolf, describing her sighting of the crumple horned snorkack.
Somewhere else in the world, away from a Wizarding Britain in mourning, a black haired man with a too wide smile hold hands with a little blond woman. They walk together, seemingly nowhere.
Maybe they find happiness, or maybe they get close. Perhaps they regret what they've done, or perhaps they don't.
Whatever else, they have their favorite vice.
Maybe that is enough.
(They were always a habit they never could kick)