Luke realized there was nothing he could do. Nothing. Absolutely. His services to the Republic and the rebels were high, but on the other side of the scale were Vader's services to the Empire, and they were much more significant. The Emperor was dead, but this did not automatically mean that the Empire had died. Not at all. She has too many allies left, and Darth Vader, if he were free, would find a way to force them to recognize themselves as Emperor and unite against the rebels under his leadership. Probably, few would have experienced the joy of the fact that the Sith Lord, known for his cruelty, ascended the throne, and, most likely, there would have been many opponents of this. But something suggested that Vader could persuade them - for example, by twisting them into an arc - in this position it is difficult to argue...