By Pass Surgery Vs Angioplasty
This forum is for questions and support regarding heart issues such as: Angina, Angioplasty, Arrhythmia, Bypass Surgery, Cardiomyopathy, Coronary Artery Disease, Defibrillator, Heart Attack, Heart Disease, High Blood Pressure, Mitral Valve, Pacemaker, PAD, Stenosis, Stress Tests

I have a similar problem with a longstanding 100% blockage of the RCA (well collateralized), a 70-90% ostial occlusion of the circumflex and a "cratered" plaque in my left main.
My take on the RCA is to leave it alone. They are very hard to open using traditional angioplasty, and even when opened, have a high rate of re-occlusion. With the collateralization your father has, it probably doesn't pose a problem and is not worth the risk.
The LAD is most likely the source of your father's increasing angina and should be the primary focus. If you want to intervene, probably the first stop there is a drug coated stent - they seem to have pretty good success in the LAD.
Whatever is done, the progression of your father's disease needs to be stopped. It's becoming fairly clear that aggressive cholesterol control via modern drug therapy with moderate daily exercise will stop the disease. In my case, I have been on Lipitor + Niaspan + Welchol for several years and continue to live in good health with good physical ability.
After 2 failed attempts to open my RCA, I finally decided that it wasn't worth it. It's quite amazing how the heart has formed it's own bypass over the years.
Best Regards