Train hard, study, well personally I'm not much for studying, but ok study hard, and party hard. But seriously, I'm actually trying to make a point. It's not so much about what you don't do as it is about what you do( I feel that people nowadays focus more and more on what they don't do and less and less on what they do). If you party on the weekends, trust me it's not that big of a deal, just try to run hard, preferable the same day as you party, and then just a short recovery run the day after and you wont miss a lot. I don't think smoking is that big of a deal either. I actually made a thread about my theory that smoking only decreases performance for slow runners (my theory is that fast runners have higher lung capacity than they need, and therefor losing a little doesn't matter), I personally smoke a pack a day just cause I'm trying to prove this point(+ I'm a idiot, don't take advice from me lol), but I might be a bit slower than you so...(also I'm older).
You're saying you want to see how far you can go. But to see how far you can go you need to train for a long time(many years). Personally I think it's really really hard to train with 100% dedication for such a long time when you don't even know if you will even make it. That's why I think it can be better to train with 90% dedication, but do it for years on, till you are at a very high level, and for going from that high level till the highest level possible(for you) you then train at 100% for the time it takes, knowing 100% that it is worth it.
So if you want to party, there's no reason not to, but that doesn't mean you should stop running. If you want to focus more on studying, well maybe that's a good idea because studying is much more likely to end in getting you money in the future, and is more important for living a good life(but it's definitively not necessary).
What's the biggest reason you want to quit running competitively? To study more or to party more(or be more social etc.)?