Dominic, I see what you mean; of course his presence is not necessary. But you said in your earlier post that he “does not belong in this movie.” That’s a bit hyperbole, I think, and implies that his presence is damaging. I just wonder in what way you think his presence is damaging to the film.
It depends what you consider damaging. Vader’s scene is the most obvious reshoot material because he never meets the heroes face to face. It comes across as a very last minute addition (which it is). It also overturns their sacrifice by making the audience root for him instead. If he was written into the story effectively it might work, but it’s just an effects scene. To me Vader isn’t the sort of character who would even consider using his lightsaber this way, he’s too cool and collected. The ending should be about people with shades of grey feeling they have achieved something bigger than their own selfish ideals. Instead it’s just a spectacle, they hug, they die, now here’s a epic as hell lightsaber massacre ohhhooo yeaaahhhh. Oh but hope. It’s about hope.