Fortunado did not realize he was being tricked. You might have him start to be suspicious when Montresor produces the trowel. He is quite drunk by then though. He definitely wakes up and sobers up by the time Montresor is bricking him in, so you could have him thinking that he hopes it's a cruel joke until he actually dies.
I agree with access teacher. This story is so powerful because it's told by the unreliable source of the first person narrator named Montressor. There wouldn't be much of a story from Fortunato's point of view. Most of us could imagine what he would say or think, so it would be of any interest. The one exception would be if he could relate to the audience exactly what he'd done to make Montressor angry.
Perhaps as Fortunato begins to sober up, he may well be like the Count of Monte Cristo who was cast into a dungeon to die. Why? Why am I here? What have I done?
You could write the story from this point and make it an interior monologue as Fortunato, faced with death, flashes back to various incidents which must have been perceived as "insults" by Montesor.
Take the perspective of the dying man who sees his life before him and seeks reasons.
In truth, this would be a very short story. Fortunato appears to be virtually clueless until the last few minutes, so there wouldn't be a whole lot to say other than plot elements such as his coughing or the dampness of the catacombs. In those last few moments of his life, there is clearly a sobering realization. He might have guessed at the cause, or he might still be as clueless as the rest of us about what he did to deserve such a fate. Your choice.
In order to rewrite an ending from a different perspective, put yourself in that character's place. You might start at the point when Fortunato has been chained to the wall. Consider that he has been drinking. What is he thinking when he first realizes what Montresor has done? Reread the ending and tell what Fortunato is thinking and feeling in response to what Montresor does and says. Also look at what Fortunato says and then give the thoughts that are going through his mind that prompt him to say what he does. Be sure you don't change the story line. You are looking to change the point of view only so the reader knows what Fortunato is thinking and feeling up to the very end. As you reread the ending, ask yourself what you would be thinking and feeling and then respond.
To be honest, I think one of the tremendous strengths of this story focuses on the way it ends as Montresor bricks in his enemy for all eternity. The last words of the story, "In pace requiescat", which of course mean "May he rest in peace," are significant in a number of different ways. We need to remember that one possibility of viewing this story is that we can examine it psychologically and symbolically. Montresor, by killing Fortunato and bricking him up in the deep dark catacombs of the Montresor family, has given free reign to his murderous instincts and given in to his deepest, darkest desires and inclinations by killing his "enemy" in such a shocking way. Now that he has bricked him in he has conveniently locked away the evidence of the murderous desires that he has given free rein to. The three last words are ambiguous, in that they can have more than one possible meaning - we are not sure whether they refer to Fortunato, shackled and bricked in, or the darker side of Montresor, which likewise is now only evidenced by a dead body that no one will ever probably find. This is why the ending is so powerful, because it points towards the same darker instincts in all of us at some level, and suggests that behind the masks that we all put on (and remember it is Carnaval time during the story), there lies a far more sinister and evil presence. This is a key theme in the work of Poe, who, as a Dark Romantic, always stressed the capacity of humanity to commit evil acts.
To write an ending could possibly be outside the scope of the purpose of this site. It would be easy to put yourself in the shoes of Fortunato, and decide how he sees the world first. Decide what type of person he is and if he has any biases, they would make him more personable,