After "The Birnam Wood" episode, we started getting attacked for killing off Leo. So if you want to be unspoiled, don't assume anything. The Chinese have a saying about never assuming your enemy is dead until you see his head on a pike and his widow weeping beneath it. That might also serve for fictional characters unless the actor wants to do other things. In this case I recommend that you keep watching and see what happens. John Spencer has not left the cast.