I have a theory where Natasha surgically swaps her face* with Yelena, and as this movie most likely takes place in 2017 (between civil war and infinity war) it will have been 'yelena' who dies at Vormir, rather than natasha. When people say that the black widow film will pass the baton to Florence Pugh, it will still technically be Natasha Romanoff, just with Yelena's (Pugh's) face.
The first bit of the theory, ending at * was an idea that Erik Voss from new rockstars had