Look, it's all about the structure of the ending. You can't take the Florence scene in isolation. You have to put it in the context of the scenes around it, which are clearly not visions or dreams. It sure looks like Batman is dead, but . . .
1) Lucius: Hey, Bruce fixed the autopilot before the fatal flight. Could it be?
2) Gordon: Hey, where did this brand-new Bat-Signal come from. Could it be?
3) Blake: What's that, you say that pearl necklace disappeared again? Could it be?
Gee, what could this all mean? Do you think that . . .
4) Yes! Bruce is still alive, which is just what all the other scenes were setting up.
That's the whole point of all those other epilogues. Along with Blake becoming the next Batman, it's the payoff to all the hints they were dropping in the other scenes.
You have to pay attention to the structure of the ending, not just the Alfred scene on its own.