Buses will run from the MK until at least 9:00 p.m. if the MK closes at 8:00 p.m. If you get done in time, monorail to MK and then bus back to POP is the best route.
If EPCOT is open late you could monorail around to the TTC, transfer to the EPCOT monorail and then bus from there to POP. You also could bus to DHS if it is open and transfer there. DTD is the other place you could transfer,
If the MK is closed you really might do better with a cab. The other options on Disney transport are fine and free, but they will take some time.