Booker in each different reality ended up becoming either himself as we know him or Comstock. So, in Infinite, the plot follows him discovering that Comstock has broken in through another reality using the "tears" between dimensions and set himself up as the dictator. In the end, Booker realized that the only way to kill Comstock is to go back through a tear and kill himself at the junction of his life where he decided which path he went down. For some reason, his consciousness switched yet again into a universe where he had never made that choice between Booker or Comstock, a universe where (presumably) tears didn't exist.

Possible indeed.

Possible spoilers? That would be like having a title that reads "London Nuked? (possible injury)"

Spoilers: First of all, haze yourself for posting that title. Second, they split realities at the baptism. Gameplay-Booker walked away from the baptism, Anna was kidnapped, and he went to Columbia. Comstock-Booker accepted the baptism, became a radical fundamentalist, created Columbia (all in another universe), and then when it was discovered he couldn't conceive children he used the Lutece siblings' research to open a portal to a parallel universe and steal gameplay-Booker's child. Using the same portal research he was able to glimpse the future and thus 'prophesy' of a future in which Columbia descends and "rains fire" on the Earth. When gameplay-Booker kills Comstock, he doesn't accomplish anything, really. In order to really stop Comstock and reverse the damage, he has to kill himself, at the time of his baptism. Elizabeth leads him there after realizing her abilities once you destroy the machine sapping her energy. He then lets himself be killed (during the baptism), thus preventing the timeline from producing Comstock-Booker. Then, the only Booker left is the gameplay-Booker when Anna was a baby.

I sincerely hope you get banned for this. I might have beaten the game months and months ago, but it's the principle of the thing.

Spoiler ahead: [spoiler]Yes, Booker DeWitt is actually Zachary Comstock. This ties in to the whole theory of trans-dimensional reality that is portrayed by Elizabeth's opening tears and the Lutece Twins, etc. How is this possible? Booker sold his daughter, Anna DeWitt (who is actually Elizabeth) so he could pay off a gambling debt. When this happened, he lost all chances of being with his daughter. In another reality, he chooses to become baptized after the battle of Wounded Knee. Thus, he becomes Zachary Hale Comstock, and orders Robert Lutece to use a machine to open a tear and retrieve his daughter. In the end, their goal is to "smother Comstock in his crib," and we see this happen when Booker is drowned in the river. The baptism is where Comstock was born and Booker died.[/spoiler]