He is gone. Utterly and forever. And I don't miss him. He claims to be a Jedi but he uses Force lighting to my poor Operative. Logic?
First of all, he is not gone forever. I have no doubt he'll be back in some way, shape, or form. You can count on it. No body, no proof of death.
Secondly, your logic is flawed; Force Lightning =/= Sith
Many Jedi used Force Lightning in their lifetimes, including Jolee Bindo, Meetra Surik, Vrook Lamar, Quinlan Vos, Plo Koon, Jaden Korr, Galen Marek, Kyle Katarn, and even Luke Skywalker himself.