Wondrous story! I see so many other reviewers noted the things I would have said, so I won't repeat their comments, but I adore the uplifting ending, particularly after the letter from Severus, in which I could literally feel a punch to my stomach.
Your sullen/obsessive Ron was too, too perfect!
I thought it was Severus killing off the other Death Eaters, but like a true mystery, your story managed to still surprise me with the hows.