I'm very sorry for your own personal tragedy in your life.
No matter how close these things get to us it should not allow us to blame other people for our own actions. Or blame other's for the actions of our loved ones.
I know it seems like if your father had the help he needed that he would of been better.
The fact is people all around this country kill themselves everyday even after receiving all the help in the world. That's because they make a personal choice that life isn't worth living anymore. No amount of help can ever change that decision. As one person said. You either get busy living or you get busy dying.
Since I believe in God I have to stem my idea from what I know is my basic understanding of the bible.
Either you have to believe that since suicide sends you to hell that everyone has free will and is responsible for their own choice regardless of circumstances... or... you have to believe that God puts people on this planet to commit horrible acts that in some way don't affect them(ie soulless or automatically absolved because of their forced event) in order to influence other's or make some of impact on those people around that person in order to teach some sort of "lesson".
The 2nd may seem far fetched.. but if you think mental illness has no cure and is not the fault of the individual then you have to believe the 2nd.. that there is no capacity for change.
You need a lesson about brain chemistry. MOST people who have severe depression, also have deficiencies in chemicals in the brain. Given chemicals, the depression can go away, and save their lives.