This would indicate a major twist ahead for Endgame, as well as a stronger tie-in to the events of Captain Marvel.
The Captain Marvel mid-credits scene shows Carol Danvers coming face to face with Black Widow, and immediately asking where Fury was.
And perhaps the real Captain is still somewhere in the cosmos, and therefore able to rescue Tony Stark and Nebula from their precarious position stranded in space.
But a new theory indicates it might not be Carol at all, but yet another shape shifting Skrull.