Hi My Uncle (54) Took A Heart Attack Today And

Hi my uncle (54) took a heart attack today and doctors put him on breathing tubes. They took them away to see how he got on and he couldnt breathe on his own. They put him on a coma and is on life support. They are going to take him off life support in the morning to see if he can breathe himself. They say if he wakes up he will have brain damage. What are the chances of people surviving from this. There is a historyof heart problems in my family and they have all passed away due to heart attacks. Please advise. Thank you.