The roles in the Graveyard are not put back into the game. Essentially, there can be more than one Harlequin in a game (and if there is only one, they don't want to die). Also, Amnesiac can take Harlequin's role if all Harlequin are dead. So there are many ways for Harlequin to win with these conditions. The point to this win condition is that the Harlequin won't be suicidal and keep on screwing with the game.
This would be a potentially hilarious sandbox role. Oh, maf is on autowin? Whoops! Killed the Harlequin. You're now the Amnesiac! Should probably be limited to night kills though.