Black Widow's death in Captain Rogers' Endgame fates were generally well-received, the way Natasha Romanoff's arc wrapped up was met with a divisive response.
After Thanos' snap and eventual death in the garden in Endgame, the Avengers were forced to sit on their failure to stop the villain for five years, coming to that there was no way to undo the decimation. All the surviving heroes went their own separate ways; each of them spending their time differently. Steve Rogers tried moving on; Thor totally shut down and went into a depressive episode; Bruce Banner used the time to create the Smart Hulk, Hawkeye went on his own rampage to deal with his losses, and Iron Man focused on his family. Nat, on the other hand, kept the Avengers semi-functional. She led regular briefings with their allies who were scattered throughout the galaxy, all while she was personally struggling with the loss of both friends and allies. So when the idea of the time heist came, the excitement and optimism on Nat's part was palpable.
This was one of the reasons why Black Widow dying in Vormir was so heartbreaking; she didn't even see the defeat of Thanos and the return of those who were snapped out of existence. However, there's one brief moment in Endgame that, in hindsight, makes her death more tragic. As the surviving team, all decked out in their nano-suits, gathered around the Quantum machine and as Captain Rogers finished his rousing speech, there's palpable excitement on Nat's part to get into the time heist. Just before they all jumped into the Quantum Realm she giddily told everyone: "see you in a minute." At this point in the film, no one had an inkling that she's not going to be able to come back to the main MCU timeline after executing their missions and collecting their assigned Infinity Stones. This also highlighted just how optimistic about the operation she was; despite not really knowing what was ahead of them, she had faith that it would work.
Given how much content Endgame had to cover, it ittedly had to gloss over certain elements of the film. That included a deeper dive into Nat's personal story in the five years since the Blip. Granted, the movie showed how hard the failure was on Nat, particularly through her emotional conversation with Steve. However, it's also not a secret that there could have been more of those scenes. Footage used in trailers showed more of her in the Avengers HQ mulling over the Avengers' defeat, and some of this didn't make it in the theatrical cut. Looking back, the film could've better established Nat's personal struggles with the aftermath of the snap for her sacrifice in Vormir to be more effective. Her happiness and excitement at the thought of bringing back those affected by the snap makes her death so much more heartbreaking.
Now, it's up to Nat’s controversial death in Avengers: Endgame. Despite being set prior to the arrival of Thanos, the Cate Shortland movie is expected to better explain what really drove the hero to adamantly give up her life for the time heist. Based on the initial social media reactions for the solo blockbuster, it may have successfully accomplished that.
