What are the consequences a teen alcoholic may face if he does not get himself treated?

Liver Cirrhosis. Alcoholics destroy their liver if they continue drinking for a long time. Abdominal enlargement with ascitis and jaundice and pedal edema occurs leading to right heart failure.
Many. Increased risk of death due to health related consequences - overdose, aspiration pneumonia, abuse of other substances, accidents due to drunk driving. Legal troubles/social troubles - dropping out of school, polysubstance abuse, premature sexual relationships etc.