Yeah, you're right. If you kill Savage in 2016, he still exists in 2015, 1959, 1209, etc. I guess my theory is more for the future timelines. Savage existed in 2146 or whatever and ended the World, but if you stopped him in 2016, that future never happens, thus Rip never has to come to the past. Time loop. Happens in every time travel movie/tv show. So you have to have some kind of starting point, which is what I meant by Earth 1 being Earth Prime. Earth Prime's ego is so massive that it is the catalyst for all future events.I mean, that makes sense, but it shouldn't affect Vandal Savage from before he was killed, similar to how Damien Darhk is still alive. Only Eobard gets the ol' "Fuck it; Speed Force," defense for still being (and how the hell did he run underwater and into a U-boat?).
On another note, this version of Darhk is so much better than the Arrow S4 version. I'm glad he kicked the crap out of Sara (who somehow beat Vandal Savage, which was also stupid), and I really want to see him fight a pre-nerf Ra's al Ghul.
I guess the Vandal Savage problem could be theorized that if you kill him at any time, he somehow vanishes from all timelines? As if he never existed? That doesn't really work either, but it's all I have.