My belief is that people (at least for a couple years) will still binge drink before they go to the stadium and just continue the party at the stadium the difference being now they can buy alcohol rather than smuggle it in. On top of that, you will have tons of people who otherwise wouldn't include alcohol as part of they game day experience who will now drink because its convenient to.
People will also continue to smuggle liquor to drink after the stadium stops selling at the end of the 3rd.
I see a couple year bump in excessive drinking happening before anything subsides.
It will be real interesting to see what if any affect it will have at basketball or baseball games since my experience at both was always no urge to drink at all. You don't see many people smuggling booze into those, at least not nearly at the rate of football games.