What Causes Sudden Demise Of A Lung Cancer Patient Suffering With Septic Pneumonia?

My dad was released from the hospital a few weeks ago after suffering from septic pneumonia he got after receiving chemo for his stage 3 lung cancer. He had a known triple A and was on Coumadin did afib. During his stay he complained of the worst heartburn ever had problems swallowing and was also in uncontrolled a fib during his stay. They sent him home with his INR high and gave him viscous lidocaine for his heartburn. He was at home for about seven hours before my mom heard him cough and found him dead with massive amounts of blood from his mouth and nose. I would like to know what could have been the likely cause of death. I am a RN and I just need to know if my thoughts are right in what I think he died from. I will also add he had 11 stents in his heart as well.