Alcohol is a mood-altering drug, the long-term effects of which take a while to wear off. He needs to give it some time before deciding whether he can cope or not. After detox and treatment, he may find the world a much brighter, better place after all.
Be aware that I only know of this academically, not from personal experience. Doesn't my comments any less true, but it does make my understanding more limited than it would be.
You are correct that our friend is getting a little ahead of himself at this point, and projecting his thoughts and feelings into the future.
No doubt he will be a different person in a few ways by the time he kicks the addiction, but what he likes about himself will not be taken away, it is this part that will be multiplied.