This happened last weekend from Saturday into Sunday. They said it was the North Quad and then the High Peaks Chair. The guy that got stuck said it was the North Quad so that's who I believe. Took one last run down that side and then the lift stopped going when he was coming back up. Was found at 8am when the lift was started in the morning. Scary stuff.
The lift in question is the North Quad. It's on a section of the mountain where you ski down into an isolated area and then have to ride a lift back to the main mountain. These kind of lifts are always where something like this is most likely to occur.
Fixed grips don't need to have both stations manned to start and shut down, just the drive. The North Quad is top drive. When they close that lift for the night, patrol ropes off all the trails down to it at 3:45pm. Then they ski down and sweep them. Once all of them are at the bottom, they get on the lift and then the bottom attendant also gets on and radios his chair number as "Last Chair". The return and load point is left unmanned while the lift is running to get them to the top. When they get to the top, the lift is shut down and the lift staff rides down the ADK Express. This has to be how that lift is closed because if they had both stations manned this wouldn't have happened.
During that time when the lift is running and the bottom is unmanned, anyone who ducked the rope or ended up behind sweep for any reason will end up at the lift after "Last Chair" went up. If they don't pick up on the fact that there's no operator and get on anyways, the lift will stop before they reach the top and they will be stranded.
It is fully the resort's responsibility to make sure no one is on the lift when they shut it down for the night, so this guy will likely sue and win. Even if the lift was closed and clearly marked, they should still be watching it and making 100% sure that no one is on it. Some mountains will even have patrol ski under the lift to make sure that the line is clear after they have shut it down.
Killington had a similar incident where a hiker got on the K1 gondola going down and was stranded for 5 hours. She got 750k after taking them to court. Even if the rope is up, if people see the gondola doors open, they will assume that it's ok to get on. Whiteface has a closing procedure for their gondola that prevents this. When they close the lift and put the rope up, ski patrol gets on after and radios in their cabin number. Immediately after ski patrol goes up, the door open rail at the bottom is disabled to ensure that no one else gets on. A guy watches the incoming cabins and manually opens the doors for anyone who is downloading. Once they reach the top, last cabin is called for the downhill line and everyone except one mechanic gets on and rides down. The lift is top drive and both stations need to be manned at all times on a detachable. The door rail at the top is also disabled as soon as last cabin is called to ensure that no one else gets on.