Answer: Darth Maul
Remember this part of Star Wars Episode I: The Phantom Menace in which a young Obi-Wan Kenobi takes on Darth Maul and ends up fighting him defeated a lightsaber fight that cuts him in half and makes him fall down a duct? There is definitely no coming back if you cut in half, and that was definitely the end of Darth Maul.
Except it was not the case. After numerous complementary but official Star Wars universe books and media, Darth Maul survived the encounter. While spin-off stories lived on Darth Maul as a Brain in a Vat (Star Wars Tales # 1
In the Clone Wars we realize that this is the last-minute case, Darth Maul used the power to pull himself into an air hole inside the air shaft, fleeing to Lotho Minor (a Junkyard planet), had his lower body rebuilt with a cybernetic suit resembling a spider's body, living in a cave like a Mad Man hermit for a decade until his brother came to find him.
So, if you thought that was the end of Darth Maul, then we apologize for having taken the satisfaction of seeing the villain die.
Courtesy of Lucasfilm.