none, because he would have been replaced with someone else.
really, it’s exactly the same arc as gollum. frodo spares him ( with old wizard’s guidance ) and it the end gollum saves the day. ( here, quigon is gandalf who only shows up once benjamin is able to find mercy within himself. quigon’s absence is the cue to us and obijamin that he’s not at peace with himself yet )
luke wasn’t strong enough - emotionally and probably power wise - to stop the emperor, and would have crossed to the dark side if he’d tried. ( just like frodo was succumbing to the ring )
that’s my understanding too. redundancy
leia opened the door during the interrogation, and confronting vader kicked it wide open. i think that’s what they were trying to say at least - but agreed the writers didn’t sell it all that well. she need more of a foil of her own, or some back story about meeting vader, something…
the story spent way too much time seesawing. they should’ve given her story more love instead