So Jack k!lls Mib and the replacement universe is what we have been watching?
No. They will tie in together. The flash-sideways are NOT season 7. They are going on at the same time and they will play into eachother.
Also, interesting that Hurley now has full memory of the island in the flash sideways. He remembered Anna-Lucias name so he has full blown memory of the island life you'd have to a.ssume.
Un-f**king-fortunatly I know this is gonna end in some cliche' bulls**t where Jack saves the f**king day, k!lls the smoke monster, and takes over Jacobs roll as the guardian of the light in the center of the island. I am going to be so pissed off if they do not do something better then that. Even if they somehow trap the smoke monster back in that light and the show ends I would not be so pissed, because you know the potential for someone to come along over the following centuries and awaken him again exists.
But the best ending for me would be Locke succeeding and destroying the island. But you just f**king know they do not have the balls to end it that way. They will do it the "happily ever after" route and pus*y out. If they do not have the balls to end it either this way, or some other bad-ass way that I do not expect, then I will be seriously let down by the show and it'll drop quite a few rungs on my all-time list.
(That is all speculation of what I hope wont/will happen. I have not read any spoilers about the finale so that is all just me taking wild guesses.)