For me, the story ends here with this beautiful shot,
An unknown future with Batman battling the Joker (we're destined to do this forever) and continuing his war on crime with other freakish rogues. A world that would exist had Ledger not died.
The Dark Knight Rises is a nice "what if" story. What if the Dent conspiracy between Batman and Gordon worked? What if Bruce Wayne decided to retire and become a hermit for 8 years? What if Alfred had actually went to Italy once a year when Bruce was gone 7 years in Batman Begins, looking to see if Wayne was happy? What if Ra's Al Ghul had a daughter? What if the League of Shadows didn't die with Ra's Al Ghul and a terrorist known as Bane and came to destroy Gotham with a sustainable energy orb invested by Wayne? What if a random kid known as John Blake saw Bruce at an orphanage and picked up immediately on the fact that Bruce was Batman?
What if Alfred told Bruce about Rachel's letter? What if he found happiness?
That's how I feel about it.