I’m not an expert on Williams schematics, but it looks like there is a make/break switch associated with the flippers circuits (“CWE ON BAT MOTOR RE”—I assume that “CWE” means “closed when engaged” and that this label applies to the circuit to the bat relay only). The switch leading to the flippers circuits would be closed when the bat relay motor is not engaged and when flipper buttons are pressed. And so, if this interpretation is correct, the flippers would still be active when the final ball drains as the bat motor relay is not engaged at this point (since the inning counter is at 5 and opens the circuit to this relay). As far as I know, all Gottliebs from this era worked the same way (i.e., flippers still work after last ball is played) and suspect the same is true for Williams machines.