I'm so sorry that you are going through this. My father was an alcoholic for most of my life and he eventually died a few years ago. As a RN and someone who has actually been through this with a family member, I can tell you that no part of this is easy. Build a strong support system for yourself (your family and friends, Alanon, etc.) to help you get through this.
First of all, his doctor will not (or should not) give you any information without your father's permission. The HIPAA laws are very strict for patient confidentiality. If you dad signed a HIPAA form at the doctor's office giving permission for anyone else to get his medical information, then the physician can only give information to whoever is listed on that form.
Unfortunately, I agree with you that an intervention may not work at this stage since your dad is still in denial of there being a problem. My father quit drinking a couple times after hitting "rock bottom" only to go back to drinking a few months later. As you know, alcoholism is a disease and it is extremely difficult for an addict to stop drinking and then stay sober- it's not impossible, just difficult, but he has to be willing to do it.
As far as your dad's health, it's hard to say exactly how his disease will progress. Liver failure can happen quickly or take a while. People with end-stage liver failure have very yellow skin and eyes (jaundice), extremely swollen abdomens (they can look 8 or 9 months pregnant!), and will have dark, concentrated urine. In addition, they will usually be confused because of the hepatic encephalopathy. Despite his years of drinking (probably at least 15 years), my dad never developed liver disease. Long-term alcoholism can also cause other problems like dementia that is not related to liver failure, but simply related to the long-term use of alcohol. That was my dad's problem- he had alcohol-related dementia (Korsakoff's dementia). Unfortunately, the only person who can give you a true prognosis is your dad's physician since each patient is different and unique, but it sounds to me like he might be in the earlier stages of the disease.
Again, I'm so sorry to hear that you are going through this- I truly know how difficult this type of situation is. If you need anything, please feel free to private message me- I dealt with this for my entire childhood as well as my adult life.