Looking for some numbers, I came across this research paper.
here is the abstract:
BACKGROUND: The present study investigated histories of prior psychiatric treatment in cases of sudden death reported to the coroner.
METHODS: A matching survey linked the register of deaths reported to the coroner with a comprehensive statewide psychiatric case register covering both in-patient and community-based services.
RESULTS: Sudden death was five times higher in people with histories of psychiatric contact. Suicide accounted for part of this excess mortality but deaths from natural causes and accidents were also elevated. Schizophrenic and affective disorders had similar suicide rates. Co-morbid substance misuse doubled the risk of sudden death in affective and schizophrenic disorders.
CONCLUSIONS: The rates of sudden death are sufficiently elevated to raise questions about current priorities in mental health care. There is a need both for greater attention to suicide risk, most notably among young people with schizophrenia, to the early detection of cardiovascular disorders and to the vigorous management of co-morbid substance misuse.
They dare not ask the obvious question.