In 1984, what makes Winston believe that proles are immortal?
Winston is caught up looking at the woman in the yard below the room over Charington's shop and he is caught in the reverie of trying to imagine what her life must have been. He is also struck by what he perceives as her beauty even though she is old and reddened and fat and hardened over time.
But it is because of her apparently eternal optimism, still evident in her singing after years and years of bearing and then caring for children and then grandchildren and even now as she toils unceasingly she sings. And so Winston believes that the proles or the concept of them is eternal, what could ever destroy this stalwart woman and her kind?