For those of you who want to know: Laura finds her son from the basement...but he is dead from hypothermia and starvation after being trapped there for weeks. In her grief Laura overdoses with her son's HIV medicines and is reunited with Simon in death, where she becomes a matron for the orphan ghosts Personally I always start crying when the kids say "She's grown older, just like Wendy!" (Reference to Peter Pan which was their bedtime story)
Actually it is hinted that he died the very first night by falling from the stairs. Evidence of this is the broken handle and the flashback that Laura had about listening to noises through a wall; immediately after the memories fade away we see the broken stairway railing and Simon lying on the floor, his neck at an unnatural angle. Which makes everything a lot sadder and creepier.
In either case, it was basically HER fault that Simon died.
To this troper the implications were that she accidentally trapped Simon in the cellar with the steel pipes, and he tore the handle off in desparation before succumbing to dehydration. She still killed him after a fashion, and his death wasn't fast. Much more horrible, that way.
No, it was definitely the fall that killed him - necks do NOT bend that way. She still caused it, as he only fell due to her accidentally trapping him inside. Sudden, but still about as close to directly being her fault as possible without... actually being her fault.
Personally, I don't blame Laura for Simon's death. He decided to hide in the basement after pushing her into the bathroom and she didn't really cause him to fall to his death. He merely slipped and fell.