What would have been cool, while at the same time avoiding the question of why Palpatine has a bottomless pit in his office, would be if Vader had picked up Luke's green saber and used it to cut down the Emperor, coming at him through a barrage of lightning through the sheer will to redeem himself and save Luke.
Not much different from the movie, but it would have been more impressive a feat than just tossing Palps over the rail.