Rogue One: A Star Wars Story initially only planned to kill one main character instead of all of them. Released back in 2016, the Gareth Edwards-directed Rogue One was the first Star Wars spin-off film and focused on the team that stole the Death Star schematics for the Rebel Alliance. Despite a bumpy production history that saw Tony Gilroy come in to complete reshoots, Rogue One was a success for Disney's revived Star Wars franchise. The film scored a 84% on Rotten Tomatoes and grossed over $1.05 billion worldwide. Fans were pleasantly surprised with the way Rogue One filled in more of the Star Wars mythology, all while feeling less like a typical Star Wars film and more like a war film in the vein of Saving Private Ryan.
Rogue One starred Felicity Jones as Jyn Erso and Diego Luna as Cassian Andor, as well as Donnie Yen, Jiang Wen, Riz Ahmed, and Alan Tudyk. They made up the main group of rebels who recovered the Death Star plans at the expense of their own lives. Fans were shocked when every single one of the main characters ended up dying in Rogue One's final battle, even if some already suspected they wouldn't make it out alive. This makes Rogue One arguably one of the most tragic Star Wars films ever, but many still praised the bold choice.
Originally, however, Rogue One had a far happier ending. An early version of the script didn't have anyone die and instead ended with a wedding. This changed later on, as revealed by writers Gary Whitta and Chris Weitz during a live Q&A session for Rogue One hosted by IGN. Edwards and Whitta originally came up with the idea to kill everyone in Rogue One, but they were convinced Disney would never allow it. Instead, they opted to just have Tudyk's droid K-2SO die in a blaze of glory.
Later on, however, Gilroy and Weitz were brought on for rewrites, and they ultimately decided to have everyone die. Disney and Lucasfilm liked this ending so much, they allowed it to happen. This is a clear example of how much Rogue One changed throughout production, and how some of those changes were definitely for the better. It's hard to say how people would've responded to the happier ending, but there's a good chance it wouldn't have been as well-received.
Disney isn't quite done with Rogue One, as a Cassian Andor prequel series is in development for Disney+. That still-untitled show is expected to film this year, though reportedly its scripts have undergone rewrites. Still, if those rewrites come out like Rogue One's, Cassian is in good hands.
Source: IGN