Ok, if they did it the smart way, this is how I see it.
Now, you say all of Batman's major villains, and Bruce, are killed, correct? And the question is, who steps up as Batman?
Dick Grayson does. He was his first and best pupil, and to honor him, he'll abandon his reign as Nightwing to Tim Drake, and get Tim to start training a new Robin. Grayson will become Batman, honor Batman in the correct ways with the funeral services and whatnot, and move into his estate with Alfred and Tim, and the new eventual Robin.
That's the only way I see things happening, with that, Grayson's death brings Tim as Batman, and Tim's death brings the "new Robin" as Batman. So forth. From then on in, there will always be a Batman, or a Batman pupil of some sort.