Have Obi-Wan kill Vader at the end of their duel in Kenobi. Then have the rest of the episode play out in full, but include a text card just before the credits roll saying this:

Through intense spiritual training with the ghost of Qui-Gon, Obi-Wan was able to master the Force. He traveled to the Imperial capital on Coruscant and slaughtered his way into the Senate chamber, killing the Emperor in front of the entire Senate. After seeing this, the Senate immediately declared Obi-Wan the new emperor, and he proceeded to bring peace and justice to the galaxy through his benevolent rule.

Kenobi is now the final installment of the Star Wars saga.