In "A Separate Peace" what symbolic role does Finny's death play in the story?

Finny was a unique character who possessed a special quality of happiness and peace that many other characters strived to have, and failed.  Genes states of Finny,

"He possessed an extra vigor, a heightened confidence in himself, a serene capacity for affection which saved him...nothing...had broken his harmonious and natural unity."

Before this, Gene explained that most people came up against something in their lives that tested them to the max, and broke them, "and they were not the same again."  For most characters in this story, it was the war.  Once they realized that there was "this overwhelmingly hostile thing in the world with them," they broke, changing forever.  However, Finny didn't.  He remained himself.  So, at last, Gene states, he broke Finny.  So when Finny dies, it symbolizes how nothing is invincible; each of us will be changed by something in the world around us-a war, a trial, even a jealous friend-and we will have to surrender our peace to that change.  It is a dismal ending; Finny represented the ability to stay happy and separate from the brutal world around us, and when he dies, the last bit of peace fled with him.  Finny symbolized peace, harmony and innocence; his death symbolized the departure of that.  It is a "growing up", a surrender to the world, and the conquest of reality over innocence.