Yes, I do think it critical that any story that features Snape and Harry must have forgivness in some form play a part. Otherwise, I do not think the story can move forward realistically. I think before HBP it was possible, but not now, not after Snape killed Dumbledore. There must be a context for that act.
Regarding the visuals: when I write I "see" all these things happen in my head. I move my character physically as if blocking a play. Therefore, I need to have a visual of them moving on the stage, so to speak. I don't want to overwhelm people with the visual, because I am, after all, a character-driven writer, but the visuals can serve the character, yes?
Thanks for very nice praise about HFN. Truly, I thought people would HATE it.