For future reference.
If you hit your head, or suffer some type of head injury, regardless of how small you think it is, go to the doctor and have it checked out.
From what i've been reading, the plane landing, blown out front tires and a violent landing? He said that he bumped his head. Laughed it off, went home, wasn't feeling well, went to bed and never woke up. This is a classic example of the results of an Intracranial hematoma. (Broken blood vessels between the brain and the skull, blood pools and has no where to go. It eventually puts pressure on the brain and if serious enough can cause death.)
Now, based on reports, and lack of an autopsy report, I can't say 100% that this is the case. I'm gonna lead in that direction though.