The dangers of open heart surgery?

My father got By-Pass Surgery for Coronary Artery Disease in February this year. He was 63 years of age and was 78 KG. Generally healthy and ok although he was diabetic. He could not come out of anaestheisia till the 5th day of Surgery. He went into psychosis and came out of psychosis on 6th day. Remained admitted in ICU till 9 days. Then shifted to the Post Surgery Ward. Then doctors told us that their are some complications and the Sternum (the bone of Chest which is Cut during Surgry to access heart) is not well (in X-Rays). So they told us that they will carry another small operation called Pectoroplasty to re-stitch the Sternum or Chest Bone. During these 15 days my dear father was not very fit. He was suffering from breathing problems, poor recovery, and pain in chest area and also very sever mouth infection such that he was not able to eat or drink much which costed alot. After 7 days he was discharged from hospital. 2nd day at home i noticed his Blood Sugar was not getting controlled and the Stitches of Chest Wound were looking abit reddish and swelled. I immediately took father to hospital and got him re-admitted. He lived out only for 10 days more even at very tight medical observations and developed many complications, his urine wasnot under control so external bag was used. He could not walk in the last days when the physiotherapist came to practise some exercising. He developed bed sores on back, head and feet inspite air bed was used. Digestion was very poor. Wound healing became worsen and worsen. at his last night, the breath of my father was so upset, high wheeze, acidosis and suddenly things went out of control. He was helped with mechanical ventilator but not to vain. At 4 am dotor just handed over me Death Certificate and the reason was "cardiovascular arrest" .