Bruce Wayne is not immortal, and as much as he is loved as batman, he will eventually have to be killed off (probably when they run out of ideas).
So, the question is, who will take his place as the perminant Batman.....?
Does Dick train a replacement for his Nightwing mantle and take up the cape and cowl for good? (Tim Drake would make a good Nightwing)
Does Damian take his father's place as the dark knight?