You have to ask yourself the basic question: Is your father someone who lives or dies? If he is an antagonistic SOB, he will probably live even if all of his coronary arteries are blocked. If he is a fighter, he can have a good life without CABG surgery or stenting.
He needs to get agressive cholesterol therapy with multiple drugs. Definitely a front line statin like Lipitor. Also to raise the HDL, high dose Niacin. Niaspan is a great drug for that and, unfortunatey, nothing better has made it to market.
Then he needs to start walking everyday as much as he can. Lean into the pain, but not too much. He also needs to start eating a lot of green stuff and not so much meat. He also needs to relax and enjoy life and learn to give the entire world the finger and just decide that he is not a person who dies and tell everyone ot buzz off.
That's what I did and I'm still living 10 years later with totally occluded arteries and doctors telling me that i would be dead in 5 years. I told them that I'm not a person that dies, so not too worry.
Depending on the anatomy of his coronary arteries he might benefit from percutaneous coronary intervention with stenting. I would ask to be seen by an interventional cardiologist first before deciding on the CABG. Because of the severity of the stenoses, especially in the LAD I would not put this off and would probably expedite the process. It is mostly the doctor's experience that allows him to estimate % stenoses. In reality there is very little difference as far as the recommendation goes between 90 and 99%.