Emperor Sheev Palpatine was dead, undeniably, irrefutably dead. He could feel his Force energy ripped from his body as it was incinerated within the core of the Death Star. Him and the line of Sith that had lived within him had been destroyed.
But he knew that was not to last, his death meant his killer would take on the Sith lineage, and he would continue on through him, the Sith would live on through Lord Vader.
But Lord Vader was no more, his heart had returned to that of Anakin Skywalker, Anakin Skywalker who was all the Sith, but whom the Sith no longer had any hold over. And even then, it mattered not, Anakin was dying, of causes none other than his own. With no one left to kill him, the line of every Sith who had lived would be ended, Anakin Skywalker was the last, and in his last moments, he had given himself back to the Light Side; the cause of the Dark Side had been lost.
As the strength fade from Anakin's body, Palpatine could feel his Force fading as well. He would not go down like this!
But there was no place left in the Universe to carry on his legacy, he could not survive, even with the power of the Force, there was too much hope in the Galaxy, the Light Side of the Force had returned, had become too strong for him to return even in the spirit.
But Palpatine had the knowledge of a thousand generations of Sith inside him. Using all the power of the Force left inside, he split the course of the Universe; branched reality, in this Universe, he would fade, but in the other, he would depart his Soul from his body, send it out to the farthest reaches of the Universe; find a place where it could survive and thrive apart from his body as it was incinerated within the Death Star, before it was too late.
As Anakin Skywalker breathed his last, the line of the Sith died with him. In this Universe, Luke Skywalker would go on to become the greatest Jedi who ever lived, leading generations throughout the Galaxy in the ways of the Force, it was truly the Return of the Jedi.
But in a further, much darker Universe, it would not be over, a Darkness in the Force continued. Someway, somehow Palpatine would return, and Luke would become known as only the Last Jedi.