Julia does not die in 1984. She survives torture, is released, and later meets Winston again.
After Winston and Julia are arrested in the room above Mr. Charrington’s shop, the Thought Police beat Julia and carry her away. Winston later asks O’Brien what has happened to her, and O’Brien tells him that she betrayed Winston and was quickly converted through torture. The decisive proof that she is alive comes near the end, when Winston runs into her in the park on a cold winter day.
By then, Julia has been physically and emotionally changed. Her body has thickened and stiffened, and Winston feels horror at the thought of sex with her. She admits that she betrayed him under torture, and Winston admits that he betrayed her too. Julia explains what Room 101 does to people: “Sometimes, [...] they threaten you with something—something you can't stand up to, can't even think about. And then you say, ‘Don't do it to me, do it to somebody else, do it to so-and-so.'” Their meeting ends with both agreeing to see each other again, though neither really intends to.
Although Julia survives, the Party destroys the love between her and Winston. Her fate exemplifies the idea that survival under totalitarian power as a kind of defeat when the person’s loyalty, desire, and self-respect have been broken.