I should be careful about distinguishing the Passion story from literature, because in reality it is only different from other literature in that it is a primary literature—the quintessence of great literature, and great art. It's pretty simple to think of a story where you find the essentially* good hero beset upon by the evil villains whose way of life he disrupted, who sacrifices himself for others, who loses everything—and who, through this very act of sacrifice, triumphs over the evil, shatters it, and, well, pretty much makes it look stupid for trying. Okay, I made it super-easy for you by already mentioning Harry Potter. But fantasy is full of such stories. There's the obvious example of The Lion, the Witch, and the Wardrobe. There's the sublime example of The Lord of the Rings. Watership Down. You can even find the thread in something as recent and popular as Ella Enchanted.
I do understand what she meant. Certainly from the Aristotelian, pre-Resurrection point of view, the tragedy is the highest form of drama.** There is a certain poetic appropriateness to the tragic ending that is hard to create with a happy one. Our minds will easily recognize the truth in tragedy, and our emotions will be moved to pathos.
“...Far more important is the Consolation of the Happy Ending. Almost I would venture to assert that all complete fairy-stories must have it. At least I would say that Tragedy is the true form of Drama, its highest function; but the opposite is true of Fairy-story. Since we do not appear to possess a word that expresses this opposite—I will call it Eucatastrophe... The consolation of fairy-stories, the joy of the happy ending: or more correctly of the good catastrophe, the sudden joyous “turn” (for there is no true end to any fairy-tale): this joy, which is one of the things which fairy-stories can produce supremely well, is not essentially “escapist,” nor “fugitive.” In its fairy-tale—or otherworld—setting, it is a sudden and miraculous grace: never to be counted on to recur. It does not deny the existence of dyscatastrophe, of sorrow and failure: the possibility of these is necessary to the joy of deliverance; it denies (in the face of much evidence, if you will) universal final defeat and in so far is evangelium, giving a fleeting glimpse of Joy, Joy beyond the walls of the world, poignant as grief.”***
“The Gospels contain a fairy-story, or a story of a larger kind which embraces all the essence of fairy-stories...among the marvels is the greatest and most complete eucatastrophe. But this story has entered History and the primary world; the desire and aspiration of sub-creation has been raised to the fulfillment of Creation. The Birth of Christ is the eucatastrophe of Man's history. The Resurrection is the eucatastrophe of the story of the Incarnation. This story begins and ends in joy... But this story is supreme; and it is true. Art has been verified. God is the Lord, of angels, and of men—and of elves. Legend and history have met and fused... But in God's kingdom the presence of the greatest does not depress the small. Story, fantasy, still go on, and should go on. The Evangelium has not abrogated legends; it has hallowed them...”****