My father had 7-bypass surgery
10 years ago and is, in general, fine today. He has had to endure several episodes of angioplasty
as well as the insertion of several stents. His heart WAS weakened prior to the surgeries however by a massive heart attack
(which is what typically incites the need for bypass surgery) that he was lucky to survive.
A VERY good cardiovascular surgeon is a must. But I would estimate that the overall survivability of bypass surgery is over 80% after 10 years (providing other health problems aren't involved).