The busses will run until the last guests are out of the park.
If it's not a crowded night, and you stay until the end of EMH, you end up on a hodge-podge bus where you just tell the driver where you're going, and he'll devise a route based on the destinations of his passengers. This happened to us one February night after the end of EMH at AK, which was absolutely deserted the last hour. When we left, the bus dispatcher was just herding everyone (there weren't many of us at all) onto one bus. We told the driver our resort, and he wrote it down on a piece of note paper.