Battlestar Galactica Season Three Conjecture
Is Starbuck really dead? I seriously doubt they would kill off a main character, especially one as popular, as Starbuck. It is possible that the actor, Katee Sackhoff, had to leave the show, for whatever reason, but I found no information to support this theory.
One conclusion, is that she must be one of the Final Five Cylons. Some may argue, that she had a mother and a childhood and therefore, cannot be a Cylon. However, that argument can be opposed by considering that memories of her mother and childhood were implanted into a Cylon version of the adult Starbuck and the original is either living somewhere else, possibly still on Caprica, or maybe died during the invasion or by some other means.
Another option, is that she didn't die, at all. She must have been rescued, some how. It appeared that she had her hand on the eject lever just before the explosion. Maybe, she ejected and was rescued by the Cylon Raider she was pursuing. To support this theory, the viewer can see the Heavy Raider, through the pursuit camera, as Apollo catches up to her. This is not from Starbuck's vision, so it stands to reason that the Raider was real, indeed. Therefore, the Raider may very well have rescued Starbuck, before her Viper was destroyed. Also, remember that the Heavy Raider can support human life, evident by the fact that Starbuck used one, to escape the red moon from an earlier episode.
Another option, is that she escaped through a stable wormhole, to Earth's Solar System. To support this theory, you just have to notice the peculiar resemblance of the gigantic planetary storm, to the Big Red Spot on Jupiter, which is also as giant planetary storm. The two, may very well be a conduit for instantaneous travel, across vast reaches of space.
One farfetched option, is the quote at the beginning of every episode, "And they have a plan". Who has a plan? The Cylons or someone else? The plan could point to a more mythical part of the story, that has yet to be revealed. Maybe, she ascends to a higher form of life to help in the effort to save humanity.
The worst option is, that Starbuck IS REALLY DEAD and GONE FOREVER, but I doubt it.