While the laws protecting bars from prosecution are pretty strong, i.e. adults have responsibility for themselves, there are many mitigating factors involved here that may cause a serious problem for Luke Bryan's bar.
1.) If he was in fact "overserved" who overserved him?
2.) If he was roofied, as some of his frat brothers suggest, is there surveillance video of him and the people near his drinks.
3.) This young man was more than overserved. He was staggering, falling, and literally bouncing off of walls. Anyone with half a conscience would make sure they have someone with them to insure their safety and the safety of others.
4.) The biggest problem is if it is true that they threw him out a back door and refused to let any of his friends come with him, that could really open them up to some serious liability. It is almost as if they did this on purpose to be cruel. They probably laughed about it (maybe still are.)
Stay away from Nashville!