My father-in-law had a quad bypass + aortic & mitral valve replacements + replacement of the ascending aorta + repair of the tricuspid, all done right before Christmas 1989, when he was 74. It was his 2nd MV replacement, first was in late 1978 or 1979, and he had quit having annual echoes & cardiac checkups.
Because he was in congestive heart failure pre-op and had retained a lot of fluid, he was not in good shape. I remember either his cardio or his surgeon telling him pre-op quite blumtly that he wasn't sure my FIL would make it through surgery, that he really needed a heart transplant.
But -- he did make it through surgery and he lived another 5 years without any further cardiac problems. (He died of cancer in August 1994, again because he avoided doctors and therefore never had a colonoscopy.) He was a widower and because he was put on Coumadin post-op to prevent clots, he was at a nursing home near us for about 6 weeks after leaving the hospital. Back then, I think, the only way to assess anticoagulation therapy was for prothrombin tests via lab draws. I'm not sure the World Health Organization had gotten the INR test instituted worldwide at that time. So, his doctors wanted him to stay in Fort Worth while he was on Coumadin. I'm sure he also had some type of rehab during that time, but I don't remember his going to a rehab facility.
Tired all the time? Heavens -- your dad **is** symptomatic. I was like that 4 years ago and thought it was "age" creeping up on me, and I was only 52. It fatigued me just to work 8 hours at a desk job. Then I had to go home & cook dinner, do laundry, etc.
Your dad can either adjust his life to his symptoms, or have surgery. Either way it's a gamble, as it is anytime surgery is involved.
He may want to see several surgeons. I've seen cardiovascular practices' websites that list surgeons specialties, and have seen some mention a special interest in geriatric surgery.