Much has been made of the unfairness of Severus Snape's demise. I have been particularly inspired by comments from the Snape-loving fans who argue that after all his sacrifice and suffering and renunciation, Snape deserves a happy ending--someone to love him.
Severus Snape is written to be loved and redeemed, but the love and redemption take place not within the text but within the experience of the reader. For the readers who love Severus Snape, there can never be real fulfillment because he is a fictional character, a creature of the imagination. But there can be real longing, as a fantasy about a fictional character is no less emotionally real than a fantasy about a living person who becomes fictionalized in the process of fantasy.
There is a similarity between loving a fictional character and loving a dead person. Both the dead and the fictional exist in the thoughts of the real and living. Rowling points to the idea that our manner of interacting with the dead is like unto the manner of interacting with fictional characters. When Harry interacts with the people brought back by the resurrection stone he is aware that they live in his imagination. At the end of Harry's interaction with the Dumbledore in the ghostly King's Cross, Harry asks
"Tell me one last thing," said Harry. "Is this real? Or has this been happening inside my head?"
to which the King's Cross Dumbledore replies
"Of course it is happening inside your head, Harry, but why on earth should that mean that it's not real?" (p723)
At the time of the Deathly Hallows, Lily Potter has been dead for about sixteen years, and yet Severus Snape continues to love her. At that point, who is the Lily that Snape loves? I think she has become a fictional reconstruction in Snape's memory. He has nursed his love, guilt and regret and in a strange way it has given meaning to his life.
Snape's unfulfilled love of Lily Potter becomes a stand-in for the reader's love of Snape. The Lily he loves is imaginary. He cannot ever find satisfaction. Likewise the reader who loves a fictional character can never find satisfaction. At best we can feel a longing, a bittersweet desire that cannot become reality.
In the tragedy of his unfulfilled love, in the longing and the throes of regret and stoic renunciation, the character of Severus Snape opens up the text to the imagination of the reader. We can share his longing and his regret in a way that we would not be able to if he were to find happiness. A happy love relationship in fiction is a closed loop. The reader becomes merely the observer and cannot really participate in the happiness of the character. She may even feel all the more lonely observing the happiness of others. A tragic love relationship on the other hand offers the reader the chance to participate by feeling compassion and possibly love for the suffering character, leading to the delicious pain of unfulfillable longing. Thus the feelings of the character within the story and the feelings of the reader about the character mirror each other. Severus Snape regrets that he could not save Lily. I regret that there will be no more Snape.
Any love Snape might have found within the text would have been a substitute for his true love. That would have been a fate far more bitter than his bittersweet revelation of heroism. The life of Severus Snape within the text is less important, I believe, than the life of Severus Snape in the imaginations of the readers. Because of his tragic love, life and death he will live on and be loved in the minds of the readers more intensely than the characters whose happiness excluded them from the sphere of our compassion.