Without getting too into it, for the sake of staying on topic, I've come to the conclusion that the Joker we see in JL is actually a 2nd clone made the same way Tim Drake was - using Cadmus technology and implanting DNA of the original Joker into an un-identified specimen. Do you really think Joker would have put all his eggs in one basket when he could have made more than one duplicate of himself? I do not think so. Yes, it's my own personal head-canon, but if you want visual consistency in the DCAU, it's the best possible explanation for why we see Joker twice in JL. The JL Joker is then killed by Ace (re-watch that scene and tell me one can't infer he's dead). Since we never see Joker after that, it all works with no issues. And in ROTJ when Bruce says he was present at Joker's death, he was technically present at both the original and the clone's death. For some reason, people get REALLY angry at me for this theory, but I don't care. At the end of the day, this stuff is all fiction anyway, so it can be subjective. I am a strong proponent of head-canon and fan theories.