Hi there. Im not a doctor.
It sounds like a serious situation reading your post. There in no point in saying anything else.
I can say though that about fifteen years ago my father in law had a Bypass surgery in a hi tech private hospital in Ireland. He had added complication of Kidney failure and was on Dialysis.
Following a triple bypass operation, he was un responsive for ten days.
I feared the worst and wondered were we being told the truth.
Like your granfather, his scan news seemed ok. If the news was bad you would have been told in the first day or two.
Anyway this may give you some small crumb of hope.
Keep the faith
Just to say he recovered on day 11 and lived for 13 years after!
God bless
Doctors were treating an immediate (acute) condition. Bypass surgery is very complex and a million things can and do go wrong through no ones fault. Clots form when your body tries to heal, if they "break lose" it can become an aneurysm. No doctor wants a patient to die and when something goes wrong they wrack their brains and work with colleagues to find a solution. I'm sure they are doing all they can and I hope he recovers!
Disclaimer: I am NOT a doctor. Do NOT rely on my opinion or advice. Batteries not included. Some assembly required.