With all of the characters involved and all of the fighting going on, basically everyone was expecting there to be a big death in Captain America: Civil War. And the movie does indeed feature the demise of a beloved character from the Marvel Cinematic Universe. However, unlike most fan theories, the major death wasn't of one of the Avengers, but of old school hero Peggy Carter. But how significant is the fact that Peggy Carter dies in Captain America: Civil War ?
In the large scheme of things, it probably doesn't mean much. This isn't the death of mover and shaker Agent Carter, this is the death of a 100-year-old woman who had not been active in anything that has gone on in the world since Iron Man came onto the scene and kicked off the current Marvel age. In fact, the only time Peggy has even appeared on screen in the modern era was when she had her tearful reunion with Captain America in The Winter Soldier, and even then she was essentially already on her deathbed. So although her death in Civil War is a heartfelt moment, I wouldn't say that it comes as a shock or has a tremendous impact on most members of the Marvel Cinematic Universe as a whole. However, it does significantly affect Captain America, and it plays a key role in the way Civil War goes down.
Peggy's death comes at a moment when tensions are building surrounding the Sokovia Accords, and Cap is feeling pressure from his teammates to sign the document. When he attends the funeral, Agent 13 gives the eulogy (revealing herself to be Peggy's niece, Sharon Carter) and repeats a quote that she attributes to her aunt, which says basically, stand your ground when you know you're right. The speech was actually spoken by Cap himself in the Civil War comic book storyline, and it serves to reaffirm to him that he is in the right path in the movie.
Peggy's death also has the unintended effect of bringing Captain America and Sharon Carter closer together. The two, who were already somewhat flirtatious, immediately bond over their connection to Peggy. This leads to a budding relationship between the pair, with Sharon covertly helping Cap in his quest to save Bucky, and the two of them eventually sharing a passionate kiss before parting ways near the end of the film.
So even though Peggy Carter's death in Civil War isn't exactly Earth-shattering, it definitely has a major effect on those who were closest to her, i.e. Captain America and Sharon Carter. And given that those two will likely see their relationship grow in future movies, I don't think we're in danger of forgetting about Peggy Carter anytime soon.