A strong theory suggests that the Grand Inquisitor still “lives” in the Star Wars canon, even during the sequel era. Tasked with leading the Imperial Inquisitorius under the command of Darth Vader himself, the Grand Inquisitor was once a guard at the Jedi Temple whom Palpatine corrupted with promises of power and forbidden knowledge. Although it seemed as though he met his end at the hands of Jedi Knight Kanan Jarrus in the first season of Star Wars Rebels, the Grand Inquisitor’s story goes much further.

https://screenrant.com/star-wars-rebels-grand-inquisitor-still-alive-sequel-era-theory/