What dangers does a man face when they've endured decades of heavy drinking, chain smoking, and frequent drug use, and has recently obtained diabetes?

Multiple conditions : With smoking he may develop COPD and Emphysema plus minus Lung cancer and many other diseases. Alcohol abuse can lead to Cirrhosis of liver and Pancreatitis. Pancreatitis can lead to Diabetes. Drug use causes many different diseases party dependent on the type of drug and mode of administration. Persons who smoke and have Diabetes are at higher risk of heart disease and stroke.

Too many to count: heavy drinking results in increased accidents, liver disease, cancer, heart disease, pancreatitis, intestinal bleeding, decreased immunity to infections and early death. Chain smoking results in bronchitis, emphysema, head/neck&lung cancer and heart/vascular disease. Depends on which drug, and whether injected, smoked etc., but ALL of them have serious side effects. Your friend needs to get help.