bypass has phenomenally high success rates, but it is a bitch of a surgery assuming they are doing the tradition rather than the new minimally invasive.
They will cut into his leg and take out the saphenous vein. They will invert that vein and use it as an arterial bypass (it will arteriolize with the change in pressure). Then they will make a vertical incision from the supraclavicular notch down to the base of the sternum. Using a bone saw, they will make a vertical cut through the sternum and then spread the sternum. Once inside, they will place the patient on a bypass machine and stop the heart. Then, they will sew the new bypass into the origin of the arteries which need bypass and then sew it to the distal site past the blockage. After they will finish, they will restart the heart, insert chest tubes, take the patient off bypass, tie the sternum closed with wires, then use either staples or stitches to sew the skin back together. In a week, assuming no complications, he'll be rehabbing and in a few months, he'll be feeling better than he had felt in yrs. It is barbaric, but it really does change quality of life. Bypass is only indicated if a patient has "triple vessel disease", meaning there are significant blockages in all 3 major coronary arteries (LAD, circumflex and RCA) or if the patient has Left Main coronary disease, which is a short stretch of an artery that gives rise to the LAD and the circumflex.