Snape is definitely the one whose death seemed the emptiest... no particular closing out there, just the knowledge that he had to die. The only part I’m sorry about was that he died thinking it was all for nothing and that Lily’s son was soon to die.
I don’t think Harry needed to apologize for his father’s actions. Harry is Harry and James was James, and I do think that most of James and Snape’s rivalry was over Lily. And most of that was Snape’s doing, I believe. I think he always felt deep down that he wasn’t good enough for Lily, it seems the sort of thing an abused child would think. And then his actions kept pushing her away. Like on some level he wanted her away from him, felt he couldn’t make her happy and James - who was everything Snape wanted to be - could.
But in the end neither man’s love was enough to save her. Her love was what ultimately saved everything, her love for Harry and the friendly shining love that young Snape saw in her from childhood influenced him to do the rest.
Presumably, her love made James grow up into a better person than he was when we saw him at 15. Her love made Snape realize what he was doing. And I think Petunia’s memory of Lily’s love is what made her take in Harry in the first place.
Well, in Rowling's case it was James and Lilly's grandson.