"Just have one drink"
For alcoholics that are starting their recovery process, any temptation is a risk. Something as small as a shot or a glass of beer can trigger that cycle again.
Therefore, don't enable their addiction by pressuring them to drink with you-especially in front of others. Be considerate and have respect for the process they're going through instead of suggesting that they have one tiny drink.
"You don't seem like an alcoholic"
Alcohol addiction has different stages which include early, chronic, and end-stage alcoholism. Some people are even able to hide their addiction well before it becomes easily noticeable.
If someone opens up to you about their addiction, recognize it as a problem rather than being in denial. If you mention that they look healthy and that there's no problem, it might encourage them to think they are still in control when they need help.
"You are going to die"
When someone has reached severe levels of addiction, health problems that could be fatal develop. This is a real concern; however, it doesn't make it better to harshly say they are going to die.
You could simply say that you are concerned about their wellbeing and that you want them to be healthy as a way of helping them maintain hope. If you want them to see the real state of their health, take them to hospital so that they can understand reality from a doctor's perspective.