There are definitely many choices, CGI, makeup, recast or re-write the story. But i found find it directly distastful if they choose to recast Leia and not very honorable of her memory, especially so close to her death. Another thing is that i don't think this would sit well with the majority of fans, Carrie Fisher played one if not the most beloved movie Princess in the history of film in one of most influential movie franchises in the history of pop culture. It's not an easy task to replace a person who been synonym with a character for almost 40 years.
The dream scenario, would be something respectful to pay her tribute. I hope to see what Fast and the Furious did for Paul Walker, to be done for Carrie Fisher.