In Avengers: Infinity War's final few minutes, Thanos snapped his fingers while wielding the completed Infinity Gauntlet and wiped out trillions of lives. In the scene which followed, we saw the Mad Titan in a dreamlike world where he confessed to a younger version of Gamora - who he murdered to get the Soul Stone - that he had enacted his horrible plan but was that a dream or something else entirely?
Well, Joe Russo has confirmed that it was the Soul Stone they were having that conversation in, something which may confirm Gamora's soul has been trapped in there and can still be recovered.
"It is [in the soul stone], it’s an orange world that they’re in. Because he’s in the Hero’s Journey in the movie, we did point that out that there’s a correlating journey in the film between Thor and Thanos. Certain characters make very human choices in the movie that are very tragic that shift the direction of the storytelling. Quill makes that choice on Titan when he punches Thanos in the face. Thor makes that choice when he plunges the axe into Thanos’ chest because he wants to tell him that he got him, that this is payback. If he had not made that decision, had he gone for the kill, they wouldn’t be in this situation. For Thanos at the end of the movie, this is part of his Hero’s Journey, we once again put him face to face with the only thing that he cared about, where he has to own up to the emotional cost of what he’s done in the movie."
The filmmaker went on to say that the child Thanos spoke to at the end of the movie was indeed Gamora's spirit (as opposed to a hallucination or something similar) but quickly changed the subject to point out that the snap actually did a considerable amount of damage to the Mad Titan himself.
"I think it’s a reflection of [Gamora’s] spirit, and the power required to use all of the stones at once is so significant that it sends Thanos into this dream state. You’ll notice his arm is damaged post the snap, the gauntlet is damaged post the snap, it’s the incredible energy required from it and only because of his strength is he able to survive actually using the gauntlet in that capacity. But it does create this cathartic moment for him."
The villain has already been stabbed through the chest by Thor and with a "damaged" arm and seemingly destroyed Infinity Gauntlet, it seems as if Earth's Mightiest Heroes may not struggle to take him down in Avengers 4. Having him feel the impact of his decision was definitely a smart move on Joe and Anthony's part, though, and it's now going to be interesting seeing how it ultimately pays off.