I feel your logic is the thing that is flawed here. The addiction to smoking comes from, as you said, nicotine. Nicotine is an active drug that makes the brain feel sedated and gives a "good" feeling. It's addicting, and your body will keep asking for more. therefor it will never stop making someone who is addicted feel good, since there is need for it and it has the "feel good" sedating effect.
WoW on the other hand, can actually become less fun. When and where differs for everyone. But at some point you will have enough of grinding, redoing the same content and what not. Some will never stop liking it. Some who stopped might think about installing it again and give it another go. But it's a given that it can become less fun, or even no fun at all. I think that might be a reason why you quit, isn't it?
As to answer your questions:
1. This is hard to answer.. Do I go back in time as the person I am now, having to convince the "me" of the past not to buy WoW because of what I've experienced (and thereby risking blowing up the space-time continuum)? To that I'd say no. I've made my choices, I have to live the consequences.
Does my mind (with all the knowledge I have now) get transferred to the person I used to be back then? I'd say yes, go for it. But I'd still buy WoW, play it with a little more decency, and change a bunch of mistakes I made in my life aswell while I'm at it. I've been a casual gamer and the game will not get in the way of my social life. Being with friends irl is just as satisfying.
2. I'll stop playing when I feel the game doesnt give me what I want from it, or there are other things that can replace it and do a better job. I do have a question for you in this case, how do you fill your time you used to spend on WoW? (partly) play other games, or something completely different?
3. I really couldnt care, there are more things then WoW, if my tv shuts down I'll go do something else, if the book I am reading ends I'll go do something else, maybe start a new book.
Maybe WoW shutting down would be a good thing someday, open your eyes to something else. But untill that day comes, I'll be logging in casually, casually do some dungeons, some quests, maybe a raid if the opportunity's there. Since that's what I like to do.