At least no causes that we can detect. Conduction abnormalities, long Q-T syndrome, there are reasons, but they don't show up on autopsy, especially 15 years after the fact.

Perhaps it was over-identification. I went to nursing school partly to care for Charlie. I know how tough nursing school is. That made me very leery of "He did this to her, that's why he wants her to die." I also have firsthand knowledge of patients in PVS. An amazingly small percentage of the brain needs to survive to keep the machinery running.