BiPoLaR, my dad had triple bypass surgery back in 1987. All went well despite a weakened heart from two heart attacks. It bought him 10 more years.
Since then, the techniques used have improved dramatically, with current methods being far less invasive and physically demanding. Some hospitals use a method where they don't even stop the heart.
Bypass surgery is considered routine these days. Nonetheless, it's a very scary prospect for patient and family.
I will keep your dad in my thoughts and prayers, confident that all will go well and you'll have him home to celebrate Christmas.
Best wishes,
Widewing