Does 5th heart bypass surgery exist?

Yes: You can have a quintuple (5x) coronary-artery bypass. For example, you can use 5 bypass grafts utilizing one artery from each arm, one from each leg, and the left internal mammary artery.

Yes: I am no sure what you are asking. If you are asking if a 5 vessel bypass surgery is possible then the answer is yes. I would guess that the most common number is 3 or 4 but certainly 5 bypasses is not unexpected. There are 3 main arteries to the heart but several branches. Sometimes we must address several branches which can increase the number of bypasses.