Booker DeWitt's death may not seem that tragic at first glance, but analyze it further and you'll see that it is in a far more existential way than usual. Upon finding out that antagonist Zachary Comstock is in fact a born again fundamentalist Booker from an alternate universe, it becomes apparent that his death is required to undue all that he has done. Accepting his fate, Booker lets alternate versions of his own daughter Elizabeth drown him at the moment before he has a chance to be reborn as Comstock. https://www.youtube.com/watch?v=y9_W503Othw It's impossible to imagine what it would feel like to learn that you are both the hero and the villain, and that the only way to fix everything, including the life of your daughter, is to die. Both versions of Booker are classically tragic characters; influenced by the atrocities they committed as a soldier at Wounded Knee. That Booker is psychologically damaged to the point of causing chaos across dimensions is sad on a whole other level, and thus makes his sacrifice of much greater significance.
