Was there ever a more unlucky soul than Fortunato? This poor devil ended up locked up in some catacombs for something he probably didn't even know that he did. Montresor never showed that he was upset, so how on earth could he apologize? Have you ever done something a little questionable and then thought to yourself, well if he looks upset then I will make it up to him only to have the person say it didn't really bother them. What are you supposed to do? Apologize for something that doesn't even bother them?
I am sure Fortunato would have made ammends but no - instead he is dead.