The ending is one reason why I liked the true version of Mysterious Stranger the best... As the book goes on, reality becomes more and more blurred until the end when everything has fallen away. The ending flows much better coupled with the story that it actually belongs to.
And also, in the No. 44 The Mysterious Stranger novel, there is no Satan; just No. 44. The Satan part of the Mysterious Stranger novella actually comes from a mix of the Chronicle of Young Satan and Schoolhouse Hill. And actually, Schoolhouse Hill, according to Wikipedia, also had Tom and Huck in it, which of course then makes sense in context with the movie.
The story has a fascinating history, and I hope to one day soon get around to reading the Chronicle of Young Satan and Schoolhouse Hill. Then I'll have read all four stories that are tied to each other.
Joy