At the end, here's what happens to each of the characters:
Rich guy Andrew Newsome has been cured (look at that smile on his face).
The Reverend Rideout has died, presumably heart strain from performing this "exorcism" of sorts.
Kat/Katherine MacDonald, Newsome's nurse, has learned that pain really is real and tangible, in short she has learned that she didn't know everything about pain that she thought she did. She also learned that unreal things can be real. This is the most important character arc of the story!
Jensen (Newsome's personal assistant) has sprayed himself in the eyes with pepper spray.
Melissa had the Little Green God of Agony start to go into her body through her eye, but had it knocked out by Kat, who then stomped on it to kill it.
But in the very last panel we learn that it has not been killed, and is alive, and is sitting on Kat's hand, in the dark. This is just a classic "BOO!" cliff-hanger ending to a scary story.