Everyone knows that Batman can never really die, but it's always fun to speculate how the Caped Crusader might meet his possible end.
When asked how he thought Batman would die, Snyder offered a scenario that current Batman readers should be familiar with, saying:
Every writer's Bruce Wayne has his own death, I guess right? They all die differently. Our version (and this is just ours) figures out a way to clone himself when he's older. He initiates a program whereby a new bruce wayne clone wakes up every 27 years. the young bruce wakes with the memories only up to the point the bat(s) comes through the window. The old bruce welcomes him to the cave, clears out his own stuff in a furnace, and the new bruce faces his own gotham and designs his own cave. own enemies, own city, etc. we showed this (me and sean murphy) in our Detective #27 story, too. Sean and I have plans to return to this story sometime in the near future.
Snyder is referring to a short story that he and artist Sean Murphy created for "Detective Comics Vol. 2 #27," a special anniversary issue, which came out last January. In the story, Snyder and Murphy explore a possible future where the Dark Knight exists centuries beyond the original Bruce Wayne's life span.
The story ended on an open note, leading many to think that Snyder would revisit this world sometime in the future. But going off of the writer's comments above, it looks like that reunion may come sooner rather than later.