Unknown. Not entirely known, but who are you fooling if you don't. Better your chances of not getting more surgery, not getting a stroke, angina, heart attack, bypass in your limbs, carotids (go to your brain), feeling better, living better and longer if you get with the program. Oh yeah, don't smoke either.
Unfortunately few. Many people with bypass surgery had it due to an unhealthy lifestyle. Old habits are hard to break. Many go right back to their old lifestyle again. Doctors also need to take part of the blame because the diet and exercise program may not have been stressed enough. Supervised cardiac rehab programs are a great way to teach folks to exercise safely after a bypass. Education classes also help.