As the epigraph foreshadows, Bella's world as she knows ends, it seems, in her choice to be transformed into a vampire and to live with Edward happily ever after. But nothing has happened yet. Before her transformation, Bella first has to get through the "painful" process of her wedding (as far as she's concerned), and then Edward promises to do his part and try to make love to her without killing her in the process. So her human world, or the world as she knows it, hasn't ended yet per se. Her choice has just set her course.
And what if her course changes? Recalling Jacob's emotional struggle in the epilogue, it's safe to assume that he might not let her go without a fight. Bella's emotional breakdown after letting Jacob go also leaves us, and even Edward, with some doubt if she indeed made the right choice. And then there's her transformation. She got cold feet once, so what if she gets cold feet again? In short, Eclipse leaves us with many questions and one answer: Breaking Dawn.