Who is most haunted by Akaky Akakeivich's corpse in "The Overcoat"?
Well, we are.
Yes, it's easy to say and prove that it's the Person of Consequence, and he seemingly learns a lesson from his run-in with AA's ghost -- at least he'll think twice before talking down to someone (of inconsequence) before thinking. We might say, in this respect, "The Overcoat" has a happy ending.
However, we as readers should remain haunted by the ghost -- perhaps not as much as the PoC. However, like AA's overcoat, the things we hold so dead in life, that define us so much as people, members of a society, persons of rank and privilege, can so easily be taken from us, by thugs, by a ghost, by chance.
The ghost is ultimately a reminder to us to think about what’s important. In Gogol’s Petersburg, alienation and isolation are the status quo, and these are maintained by hierarchy, bureaucracy, pride, greed, arrogance, etc. So, the next time we talk down to someone from a position of authority, maybe we’ll feel the corpse of Akaky pulling at our overcoats.