Really good manga. My conclusion:
Kyou fell of and died, if it was an accident or if Kagami was directly responsible for it doesn't really matter, if finished the job of fully breaking the characters. The author kept it vague, since crossing the balcony was suicidal in the first place. Anyway, Kyou being dead completely destroyed both Kagami and Riki, Riki ended up humoring Kagami being a replacement, (maybe initially it was for cope, but he was clearly fully aware of the situation by the end) and she was never alright in the first place.
About the end: Was the paranormal involved in saving them, or was it just a trick of the mind of two completely broken individuals as a coping device? I firmly belive its the latter. The characters and pieces the author had could only end in a sad note (save for an incredible asspull, or a deus ex machina), not only did they manage to commit to the story they were writing, they also came up with a sensible ending; Two completely shattered minds went on to live delusional and likely misserable life.