The Russo brothers actually answered this in an interview from this Chinese source. As the original article is in Chinese I am getting the quotes from this reddit post, although I think all that's happened is that the user ran it through Google Translate.
Q: Can you get the soul your sacrificed for the Soul Stone back when you return it?
A: No, the process is irreversible. Even if you have returned it to its original location, you wouldn't be able to get the person back. In fact, it's not really returning the stone, more like put it back properly. The tribute soul for the soul stone will forever be sealed in that place, therefore Black Widow is gone forever.
It is apparently impossible, according to Red Skull and the Hulk. I can’t remember Red Skull’s exact quote from Endgame but he says something similar in Infinity War.
Red Skull: To ensure that whoever possesses it... Understands its power... The stone demands a sacrifice.
Thanos: Of what?
Red Skull: In order to take the stone you must lose that which you love. A soul...For a soul.
Avengers: Infinity War
As in you can’t return the sacrifice because they have been traded for the Soul Stone. This makes sense when we see Hulk try and bring her back and he can’t even though he has control over all the Infinity Stones.
What is interesting though is that Cap took the Soul Stone back from where it was taken so presumably if it was placed back Nat could come back I.e. giving up the Soul Stone to have her back. That is just speculation though.