Eu gostaria de apontar para o fato de que quando Luke está fugindo com Darth Vader, a batalha já deu um grande passo em favor da aliança. O gerador Shield em Endor foi destruído, onde todos os homens dentro da Estrela da Morte sabiam que ele não estava totalmente operacional defensivamente ainda. O Star Destroyer caiu na Estrela da Morte momentos antes.
Eu posso imaginar sempre que você vê a batalha tomar uma nova direção que não está a seu favor, você vai tentar sobreviver e não nos esqueçamos que a primeira Estrela da Morte também foi derrubada.
Do script no IMSDB :
130 INT DEATH STAR - MAIN DOCKING BAY
Chaos. For the first time, the Death Star is rocked by explosions as the Rebel fleet, no longer backed against a wall, zooms over, unloading a heavy barrage. Imperial troops run in all directions, confused and desperate to escape.
In the midst of this uproar, Luke is trying to carry the enormous deadweight of his father's weakening body toward an Imperial shuttle. Finally, Luke collapses from the strain. The explosions grow louder as Vader draws him closer.
EDIT: @Boelabaal por que ele não forçou a força dele:
EMPEROR Now, young Skywalker...you will die.
Although it would not have seemed possible, the outpouring of bolts from the Emperor's fingers actually increases in intensity, the sound screaming through the room. Luke's body writhes in pain.
Vader grabs the Emperor from behind, fighting for control of the robed figure despite the Dark Lord's weakened body and gravely weakened arm. The Emperor struggles in his embrace, his bolt-shooting hands now lifted high, away from Luke. Now the white lightning arcs back to strike at Vader. He stumbles with his load as the sparks rain off his helmet and flow down over his black cape. He holds his evil master high over his head and walks to the edge of the abyss at the central core of the throne room. With one final burst of his once awesome strength, Darth Vader hurls the Emperor's body into the bottomless shaft.
The Emperor's body spins helplessly into the void, arcing as it falls into the abyss. Finally, when the body is far down the shaft, it explodes, creating a rush of air through the room.Vader's cape is whipped by the wind and he staggers, and collapses toward the bottomless hole. Luke crawls to his father's side and pulls him away from the edge of the abyss to safety. Both the young Jedi and the giant warrior are too weak to move.