This is very confusing? If the hospital said his heart was in good shape and they fixed the blood flow, then why is a third of the muscle now dead? Has he had a new test to reveal this information such as a nuclear scan?
Your father is fortunate that he had surgery that worked.
When we have heart attacks, heart tissue is either killed or stunned, and I'm sure that is what your doctor is referring to. Stunned cells can be revived with exercise and good drugs, but where the damage is done to the heart is important, considering one's recovery. I lost about 1/3 of my heart function 14 years ago and I'm still standing. I'm betting your father's doctor's reference to 5 years is just a guess. Heart bypasses can last 15 - 20 years or fail within days of the surgery, and doctors have absolutely no idea how long they will last. We have people on this board who have had bypasses last for many years, and some of us have early failures. I'd urge your father to concentrate on exercising, eating well, taking the meds and enjoying every day we are given.