I'm not a lawyer but I believe there is something called host liability which in a nutshell puts the blame on the employer if they are aware that you had a drink during work hours. If you decide to go to the bar after work and get plastered they can put partial blame on your employer in such an instance. Scary thought.
That's a matter of state law, so check that out in your home state (or wherever you may be at the time.
No matter what, though, no employer wants to be dragged into something like that. It's a PR nightmare. It's also one of the reasons that it's been years since I've attended a sponsored party that did not have a stack of cab vouchers, an open Uber account, or something along those lines. It's both cheap insurance and the right thing to do.
Regarding those bars, many states have what's called a "dram shop act" (or something similar). Such a law holds an establishment that serves alcohol responsible for the harm its customers cause when leaving (no matter what their state was when they arrived). Depending on the law, either or both the server and the establishment may be held responsible for the harm.
Many states (if not all) also have a law against serving alcohol to an intoxicated individual. Again depending on the law, the server and/or the establishment may be liable.