So ... how did Miles die? I don't quite understand.
Did anyone else get the sense that the children's uncle / guardian was dead? Mrs. Grose kept on referring to him in the past tense, and when she said odd things about him, and was pulled up by the governess, she became very embarrassed. Also, why was he so determined not to be disturbed?
I must say I was rather disappointed by this novel.
It depends on if you think the ghosts were real or not. If the ghosts were real, one could speculate that Peter Quint was responsible for Miles' death. "...and his little heart, dispossessed, had stopped." OR if the ghosts were simply the figment of a sexually repressed governess, you could draw the conclusion that Miles had a heart attack from his governess frightening him to death.
You make an interesting point about the guardian. That's something I've never explored before but I'm inclined to disagree with you there. How else could the governess land the position? However, there is the theory that Douglas is really Miles...
Why is the Uncle so determined not to be disturbed? The only answer I can come up with is that was often the way of parents back in Victorian times. They hired a governess to care for their children and then barely saw them or had little to do with them at all. I don't think he had anything terrible to hide by not seeing them.
I'm sorry you were disappointed by the novella. Maybe try one of the film versions instead? I highly reccomend The Innocents w/Deborah Kerr or the Masterpiece Theatre version from 1999 starring Jodhi May as the governess.