I suspect the best path forward is simply to cast another actress. They needed CGI for Tarkin and Leia in Rogue One because those movies dovetailed right into A

I suspect the best path forward is simply to cast another actress. They needed CGI for Tarkin and Leia in Rogue One because those movies dovetailed right into A New Hope and the appearances of the actors were a core part of the identity of the characters, but honestly, while it was great to have Carrie Fisher reprise her role as 53-year-old Leia in Episode VII, it would have been perfectly acceptable for them to have cast another actress from the start. This brings to mind the Harry Potter series. The first two movies had Richard Harris playing Dumbledore, but then he died, so they simply recast the role and gave it to someone else, without any in-universe explanation for the change in appearance. And personally, I think Michael Gambon was a much better Dumbledore than Richard Harris.