Usually surgical operations are not performed unless it is an urgent matter of survival when the health of the patient is an issue. If I remember correctly, 1 to 3% under normal conditions have complications after valve replacements. Obviously, the risk is higher with health issues.
I have severe mitral valve regurgitation for the past 5 years or more without major symptoms, and the doctor and I put off any operation as the doctor stated the expectation would be to not feel any better and there is a risk of complications effecting quality of life and not feeling very well.
It is really an individual decision, age, general health, etc. Your father may or may not feel any better, and the operation usually would not increase longivity unless the valve problem is causing heart failure, etc.