Talk to the landlord and see what they say. What you don't want to do is just disappear and not tell the landlord - do it the right way, and tell them what's going on. Otherwise, if you just leave, it costs the landlord a lot of money and it will affect your credit and ability to rent again. Do it the right way, you'll be responsible for the remainder of the lease (or in some cases until the unit is re-rented) - depends on your landlord.
Man, I'd just do a consultation with a lawyer. If you leave and drunk guy doesn't - then you could be liable for the costs of evicting him anyway (plus any damages he and his friends do) - on top of the remainder of the lease. How did he get a key? Did you give it to him?