Answer:
After Montresor completed his dreadful plan, he got back home and started to wonder about how long it would take for Fortunato to finally die and his body start decomposing. At first, Montresor was pleased, since he was now free of all hatred. However, after about thirty minutes, his humane essence made him feel like something was wrong, and then he realized he had been carried away by anger, which made him do undescribable things, which he would certainly regret later.
All of a sudden, Montresor stood up, ran to the front door of his house, opened it, and headed towards the catacombs where he had left Fortunato. He ran all the way, and was breathing with difficulty when he got there.
As soon as he saw the wall behind which Fortunato was, he grabbed a barrel of wine and started to hit it against the wall. After a few minutes, the wall was broken down. Montresor saw Fortunato there, still chained to the wall, but no longer alive.
Montresor heard a sound that seemed to be that of footsteps. He turned around and saw nothing.
Consumed with regret, he decided to have some of the wine that was in there. As soon as he grabbed one of the big bottles, it broke in pieces, and Montresor realized its content was not wine, but pure alcohol.
Then, he heard the sound of footsteps again, this time closer.
All of a sudden, the alcohol on Montresor's chest and hands, and also on the floor, caught on fire, and Montresor was then consumed by something much more painful than hatred or regret: the unforgiving flames of revenge.
Explanation:
I simply imagined what happened after the story ends in "The Cask of Amontillado," as requested. Therefore, the literary attempt above is merely a stretch of imagination.