DarkFather said:
I've spent accumulated hours thinking of a scenario of how to do this. My favorite one I've come up with is Obi-Wan Force Pushing Vader (after he was de-limbed), off a giant narrow cliff. Obi-Wan pries Vader's lightsaber from the hand on the disembodied arm, he walks to the edge of the cliff, looks down far below, but doesn't see Vader. So he assumes Vader fell straight into the river and was destroyed.
Then we don't see Vader until ANH. We don't need to know exactly where he landed. All we need to know is that Obi-Wan defeated him, and he was horrifically injured further from the lava afterwards (a given because of the new suit, iron lung, and burn marks later revealed in ROTJ).
I think it should have been more tragic. And should probably have happened at the end of Episode 2. I don't think he should have lost all his limbs at that point either. Vader has years of fighting ahead of him to lose limbs. From the time Anakin falls to the darkside to the time we meet Vader in ANH, he is suppose to have fought and killed many Jedi. That leave plenty of chances for slipups and lost appendages. It would have worked a lot better had Obi-Wan obviously beaten Anakin, knocked his saber out of his hand and then disengaged his own saber.
At this moment he could have begged Anakin to come back, to see that good that is still in him, at which point, Anakin not wanting to give up so easily reaches out with the darkside to attack Obi-Wan, they fight with the force for a bit, then suddenly and unexpectedly the ground under Anakin's feet gives way. Obi-Wan not prepared to let his best friend die lunges forward catches his arm. There is a quick, "Anakin, let me pull you up" scene, maybe a few more words exchanged, then defiantly, Anakin either reaches over with his non robotic arm and detatches his robotic one, allowing him to plumet into the black smoke below, or Obi-Wan has a hold of his good arm, and Anakin reaches over with his robotic arm and claws into Obi-Wan's arm causing him to let go.
I like the idea of him disappearing into thick clouds of smoke that we know are over a molten river, we and Obi-Wan are to assume he is dead, but it gives the possibility of him surviving. I also like the idea of Obi-Wan trying to save him up until the very end, rather than intentionally killing him. I don't think Obi-Wan would have accepted that his friend was gone forever. Also it fits with "Obi-Wan once thought as you do".
I think this should have been the climax to the second film, and that sometime near the end of the last film we should have been introduced to Darth Vader, but never be told directly that it Anakin, he is just the new right hand man of the Emperor. Sometime between films Obi-Wan figures it out, which will only be revealed to us in Return of the Jedi. In this film (ep.3) Obi-Wan should have dealt with his friends death. There could have been a touching scene where Obi goes to visit his fallen comrade's wife, she could tell him that she just found out she is pregnant, and right before he leaves he could turn to her and say, "if there is anything I can do to help, just know that I am here for you." This should have been the very last we hear of Anakin's widow in the PT. This leaves just enough connection that we can connect the dots.