There is no test to determine the cause of his liver cirrhosis unless testing reveals a condition which is a likely suspect as in my case I had hepatitis c for probably 37 years with no other risk factors.
Really what would it change things knowing the cause he still has liver cirrhosis. No matter the original cause he must never drink any alcohol and if he is overweight he must lose weight.
Common causes of cirrhosis of the liver include:
Nonalcoholic fatty liver disease
Chronic viral hepatitis (A, B, and C)
Inhereited (genetic) disorders
Primary biliary cirrhosis (PCB)
Primary sclerosing cholangitis (PSC)
Infants born without bile ducts
Less common causes of cirrhosis include:
Unusual reactions to some drugs
Prolonged exposure to toxins
Chronic heart failure (cardiac cirrhosis).
In certain parts of the world (particularly Northern Africa), infection of the liver with a parasite (schistosomiasis) is the most common cause of liver disease and cirrhosis.
Hi if he can stop the cause for his cirrhosis he may be able to survive for many years. If his cirrhosis is very advanced and the cause of his liver damage cannot be stopped he will likely need a liver transplant at some time in the future in order to survive.
Sending my best hopes for your dad and your family