I do like the idea, but I’d give it a bit of a twist. The Anakin and Darth Vader (both apprentices of Obi-Wan, with Vader having fallen in Episode II) characters fight each other in the third prequel and we don’t see the outcome. Obi-Wan would fight who we think is Vader, not knowing that it’s a fallen Anakin posing as Vader (perhaps to avoid detection by Palpatine). The duel takes place as normal, with Anakin-as-Vader sustaining critical injuries and Palpatine manipulating his memories to remember Anakin as “another person.”

However, the events of Star Wars trigger memories within Anakin-as-Vader and Obi-Wan. Obi-Wan would sense something of Anakin within Vader when he says “you should not have come back” (look at the expression on Sir Alec’s face), while Anakin-as-Vader would feel the “Skywalker connection” during the tench run. This eliminates Obi-Wan lying to Luke (as he didn’t know Vader’s true identity - Yoda did, but Yoda’s abilities are more fine-tuned than Obi-Wan’s) while giving Anakin-as-Vader a revelation that might steer him towards the light.