We left after an 8pm Fantasmic! that closed down DHS for the night, walked to EPCOT, made a WS lap, watched IllumiNations at 9:30, and walked by to DHS. At around 10pm, we had no trouble getting back to our car and getting it out of the parking lot. There were still many other cars in the lot and busses were still running. The only thing is that it was an Osbourne Lights night, so even though the posted closing time was 8pm, I think they still allow people to walk through Osbourne after they leave Fantasmic!, so the effective closing time might have been more like 9-9:30?
I'm curious--does anyone know what happens to your car if you don't remove it before the parking lot closes? Can you just go back and retrieve it in the morning or does Disney tow it? Also, there are no gates to pass through when exiting and I've never taken notice--is there a larger gate that literally locks down the parking lot entrances and exits? I know that Disney need to keep control of the parking situation, but I'd be surprised if there wasn't some reasonably easy way to retrieve your car from the spot where you parked it even if you returned after the posted parking lot closing time.