Not a dream. Notice the scar on bruce's forehead from when Bane broke his cowl. Alfred left Bruce before that fight, so he had no knowledge of the scar, and if you look close in the cafe, you can see the scar, so Alfred couldn't have imagined it. Also, look close as the Bat flies out over the bridge into the bay. There's a pair of lights that aren't on for a split second, then they turn on. I take that to mean auto pilot engaged. :D I was leaning very heavily towards Bruce died the first two times I saw it. But the third time's the charm (with slow motion instant replays).
That, and Michael Caine, the actor who played Alfred, recently confirmed that the cafe scene was real.