I know at least one person with a 100% disability rating from the US military for PTSD and have heard it is not unusual.
While suicide might seem like a cowardly way out to some, there are other sufferers who choose to take their chances with electro-shock therapy, which has experienced rejuvenated interest over the past 20 years. It should be clear, however, that anyone pursuing it has exhausted all over treatment and is still suffering to some great extent.