Reva only stabbed him in the guts, he is likely alive unless they are going to retcon most of the Star Wars Rebels storyline. My only minor gripe with the show so far is that they cast Rupert Friend in the Grand Inquisitor role instead of Jason Isaacs who voiced the character in Rebels and would have done an awesome onscreen version. The man has the pedigree to play villains onscreen; Lucius Malfoy (Harry Potter) and Col. Tavington (The Patriot).