You can walk to the Epcot International Gateway from ESPN in maybe 5 minutes. IF the park is still open you can enter (need theme park ticket) and walk through to the main entrance where the buses are located. It's a long walk, but doable. You can also either walk to the Disney Studios in maybe 15-20 minutes or boat over from the Boardwalk. The walk is faster unless you catch a boat right away. As the previous poster said, buses from there should be running until 9:30 that night if the park closes at 8:30. You do not need to enter the Studios.
Your other option if you want to stay really late is to grab a taxi from any of the Epcot resorts (Boardwalk being the closest to ESPN). Just walk through the lobby and out the main entrance. Normally taxis are waiting outside all WDW resorts. If one is not available a Cast Member will get one for you right away. Fast, convenient, and reasonable way to get back to your resort.