The passing of Carrie Fisher came as a shock to the world. The actress reprised her role as Leia from the original Star Wars trilogy in The Force Awakens, and Luscasfilm planned to have her reprise her role in Episode VIII, as well.
According to reports, the actress had completed all of her scenes in Star Wars: Episode VIII but that leaves Lucasfilm and Disney with what to do with the character in Episode IX. Colin Trevorrow, co-writer and director of the script for Episode IX, will meet with Lucasfilm president Kathleen Kennedy this week to figure out how to continue the Star Wars saga without Fisher, according to The Hollywood Reporter. The outlet also revealed that there were two key scenes planned for the next two chapters of the saga:
“Insiders tell The Hollywood Reporter that at least two key scenes are planned for Episode VIII (Dec. 15) and Episode IX (2019): a Leia reunion with Luke Skywalker (Mark Hamill) and a confrontation with Kylo Ren (Adam Driver), her son who killed Harrison Ford’s Han Solo in 2015’s The Force Awakens.”
They don’t reveal if both of those scene take place in Episode VIII or not but they are scenes that fans of the series absolutely would want to see. It was reported that Fisher was to have an even larger part in Episode IX but that is now up in the air. The events of Episode VIII are what gives her a larger part in Episode IX so there is a chance that the final cut of the film would reduce her role.
Another possibility is to leave the screenplay Trevorrow wrote as is and create a CG version of the actress in the same way Peter Cushing re-appeared in Rogue One, despite the actor passing away in 1994. Ironically a young Fisher was also given a cameo at the end of that film using the same technology.
As far as I know Episode VIII has not yet gone for reshoots and Lucasfilm has plenty of time to figure out what to do so I suspect the most likely course of action is that they’ll rewrite part of her storyline in that film to seamlessly retire the character in Episode IX. They would probably need to create a CG version of Fisher for whatever shots they can’t use from any outakes they have lying around. Much like what was done for the late Paul Walker in Furious 7.