From the beginning, Rogue One was pitched as a gritty war drama in space, and the marketing made sure to hammer that point home. Much of the imagery was reminiscent of World War II or Vietnam, so it logically fit with the tone of the film that many of the main players would meet their noble ends. Stealing the Death Star plans from a heavily-guarded Imperial data facility is very much a suicide mission, especially for a scrappy, under-funded Rebellion forced to make the best of what resources they have. One of the goals of Rogue One was to show the hardships and tremendous sacrifice of the conflict, meaning it arguably would have been inconsistent if some of the characters received a happy ending. Credit has to go to Disney for realizing this early on and allowing Edwards to make a massive tentpole where all the characters die.
Shortly after Rogue One‘s premiere, it was announced that star Felicity Jones had a sequel option in her contract, but fans shouldn’t read too much into that. The multi-picture deal has become a standard in the industry (Hugo Weaving signed one with Marvel), and it is far from a guarantee the actor or actress will make another appearance. Unless Jyn Erso shows up in the young Han Solo spinoff, it’s difficult to see where she’d fit in given that she (seemingly and likely) died on the beach. Her time in a galaxy far, far away may have been short-lived, but Jones left her mark on the legacy and became a meaningful part of the canon.