I think a lot of the assumption is that after everything to eat, buy, and ride has closed down, people wander out on their own.
That said, we were at Epcot last September and it closed after Illuminations, but we decided to walk around the showcase afterwards to let the crowds at the transportation areas thin out. We were there a good 45 min/hour after park close. There were CM's EVERYWHERE though. Nobody asked us to leave, though we thought they would, and I'm sure at some point they would have.
I remember the time before though having super late reservations at Coral Reef and we got out waaaaay after park close. There were security guards stationed at all the junctions waving goodbye, but the fact of the matter was if we wandered the wrong way, they came right over and asked if we needed help finding the front gate. LoL