I've been trying to understand how both timelines can exsit simultaniously if WHH.
So, the only way I can see this working is if our new Timeline results in the creation of the time line we've been watching for the last 5 years. This would create quite a huge loop in time, just think about time. For the sake of illustration I will use regular time and timeline X (this being our new timeline).
So Timeline X comes into existance, but for what ever reason our new Oceanic 815 crew doesn't feel right here. So they start to try to change things to make them feel more like they're suppose to be. These actions, whatever they may be will result in the creation of our regular timeline.
So our regular timeline starts 815 crashes we find ourselves back at the incident and sure enough Jughead results in the creation of Timeline X.
So Faraday's plan does work, he does prevent 815 from crashing not realizing that this is what created the universe (or the chain of events called history if you will) that he has known his whole life.
This is the only way that I can see for the original timeline to still exist along side and alternate timeline that actualy exists as well AND still end up within the rules of WHH.