Saw some folk talking about the forgiveability or lack thereof of Darth Vader, particularly wert the murder of children.
The prequel films had not been made at the time Return of the Jedi had been released, and I don't believe Lucas' claims of having planned the whole thing out from the beginning, so usually I am not interested in judging the first three Star Wars films on the basis of actions or emotions depicted in the prequels. I also don't recall Luke saying at any point that he forgave Vader for his past actions, prequel or otherwise. What I remember is Luke saying he still senses good in him, which I interpret as the potential or desire to turn away from evil and to do good.
My feeling is the idea of Vader being redeemed is not that his single act of casting down the emperor, but that it represents an internal change and a commitment on his part. That, had Vader survived, he would have devoted himself to doing good and to make what restitution he could for the evils of the empire. But his single act in the throne room doesn't make him good in itself, doesn't undo the evils of his past. It is a symbol of the change in the character and the new path he is taking, as is his ghost's appearance as Anakin later on.
I don't think it's a matter of having been forgiven and I don't think the evil Vader did in the past is or can be undone.
I do think there's a potential term collision between redemption as in 'how fans feel about a character' and redemption as in 'character internals reflected in externals'. I also suspect these opinions of mine are strongly influenced by the surrounding Christian cultural context; certainly I've had to work at not using Christian-sourced terminology in the writing of this post and probably missed some nonetheless.