This is the first theory I've posted on Dark UFO and i'm glad to contribute for the first time. This is a quick simple one.
All right, I think after tonight's episode, the island is the cork, MIB the wine, Jacob/Candidates the Bottle. if Jacob and every one of his replacements/candidates dies the bottle breaks, the cork (island) sinks and MIB is free and breaks loose around the world. So now MIB has killed Jacob and if he kills all the remaining candidates the island will sink and he'll be free.
I've kind of realize it at the end when MIB broke the bottle as a symbol of killing Jacob and everyone that stands in his way. Now, what i'm assuming is that it is the way the sideways universe was created. The question is was it created by Jughead (the explosion would have killed everyone on the island including Jacob) or something we haven't seen yet. Who knows maybe we'll see the smoke monster appear at some point in the sideways universe later in the season, he just haven't arrive in LA yet. Some people will say: «well Jack and all the candidates are alive in the flash-sideways». My answer is I don't think you can be a real candidate if you have never gotten to the island, you can be a potential one tough.
Please critic and comment. Sorry for the spelling I'm french canadian!