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human
[Star Wars] What if Vader killed the Emperor in ROTJ using another method? What do you think would happen next?

I'm not exactly sure how to word my question, at least for the title so let me explain better first. Okay, so when Luke and Vader are in the Throne Room on the Second Death Star, the Emperor is sitting in his throne and practically goads Luke into giving in to the dark side. The Emperor released his restraints, ordered the Commander to fire on one of the Rebels capital ships and the battle over Endor begins. Luke noticed his lightsaber and the Emperor notices it too, he tells him, "take your weapon! Strike me down with all of your hatred and your journey toward the dark side will be complete."

Luke was tempted too, knowing that he had to die and he did grab it with the Force and went in for the fatal strike. Then, Vader blocked the strike locking their blades together before beginning their duel. This was the perfect opportunity to kill the Emperor, the one shot Vader was waiting for and this was Darth Vader, not Anakin Skywalker, he wasn't redeemed yet. So, what if Vader killed the Emperor then? 

Let's say he did. He swung quickly and sliced the Emperor in half and doesn't duel with his son. What do you think would happen after that? Vader didn't get electrocuted, so he won't die and I don't see him and his son dueling over the situation. He also doesn't know about Leia then, he only found out when dueling with Luke. The story after this point would obviously be different, we know how Vader feels about the death star but we also know how he feels about the Rebellion, then on top of that we know he wants his son in his life, his family was the reason he became Darth Vader in the first place. Would he keep his promise and offer his son to rule as father and son again, do you think Luke would even want that?

I hope I better explained my question, and I am curious to hear what you think of this what-if scenario. Let's also assume he remains Darth Vader, he stays rooted in the dark side and proclaims himself Emperor of the Galactic Empire.
gpt
Vader is a brilliant military tactician, but a horrendous politician. Even with his son neither have the skills to lead a galactic empire. The Moffs and Admirals would quickly turn against him and the Empire decends into chaos.

Also Luke was intent on saving his father. There wasn't an option to join the Dark for Luke, it was save his father or die. Would Vader be able to strike down Luke? Maybe, but Vader never wanted his son to die. If he somehow comes back to the light side he would go into hiding, never to be seen again. He's already caused too much damage.