In a rare official statement on those rumors, Lucasfilm posted the following on the Star Wars website:
We don’t normally respond to fan or press speculation, but there is a rumor circulating that we would like to address. We want to assure our fans that Lucasfilm has no plans to digitally recreate Carrie Fisher’s performance as Princess or General Leia Organa.
Carrie Fisher was, is, and always will be a part of the Lucasfilm family. She was our princess, our general, and more importantly, our friend. We are still hurting from her loss. We cherish her memory and legacy as Princess Leia, and will always strive to honor everything she gave to Star Wars.
We probably won't know this decade what was scripted for this Leia-centric movie, but here's why it won't happen, along with apnea as the official cause of death:
Fisher’s toxicology review found evidence of cocaine, methadone, MDMA (better known as ecstasy), alcohol and opiates. The test results “suggests there was an exposure to heroin, but that the dose and time of exposure cannot be pinpointed.”
You can read the 24 page report. Should have spotted the clue in Bright Lights when she was getting in shape for Force Awakens and sneaking some Coke.
An executive: "During the making of Jurassic World, he focused a great deal of his creative energies on asserting his opinion. But because he had been personally hired by Spielberg, nobody could say, 'You’re fired.' Once that film went through the roof and he chose to do Henry, [Trevorrow] was unbearable. He had an egotistical point of view — and he was always asserting that. When the reviews for Book of Henry came out, there was immediately conjecture that Kathy was going to dump him because they weren’t thrilled with working with him anyway. He’s a difficult guy. He’s really, really, really confident. Let’s call it that."
A veteran movie producer: "There’s one gatekeeper when it comes to Star Wars and it’s Kathleen Kennedy. If you rub Kathleen Kennedy the wrong way — in any way — you’re out. You’re done. A lot of these young, new directors want to come in and say, ‘I want to do this. I want to do that.’ A lot of these guys — Lord and Miller, Colin Trevorrow — got very rich, very fast and believed a lot of their own hype. And they don’t want to play by the rules. They want to do **** differently. And Kathleen Kennedy isn’t going to **** around with that."
Plot A would progress like this: 5 years after The Last Jedi the Resistance is no longer centralized and is not a popular idea among the galaxy. Kylo Ren’s rule over the galaxy is seen by most as benevolent. Many within the Resistance itself are questioning why they should even be fighting.
Not surprisingly, Rey, Poe, Finn, and Leia are all still holding fast to the idea the galaxy should not be under empirical rule. They are tipped off by a mole inside the First Order promising that if they follow their lead, they will discover the horrifying true nature of the First Order.
The tip leads them to a planet in the unknown regions, and they must infiltrate a First Order command station to extract a young female alien prodigy who is the key to navigating these regions.
After a successful rescue of the girl who is essentially a prisoner of the First Order, they discover a planet entirely comprised of an ocean. Beneath its waters is the secret to the First Order’s unlimited resources, an ancient manufacturing station literally powered by the populations of conquered worlds of the unknown regions.
This entire A plot revolves around liberating the captives before they are exterminated and exposing these horrors to the galaxy at large. This plot is resolved with the Unknown Regions becoming united and preparing for war with the known regions.
The B plot revolves around Kylo Ren hunting down other Force users in secret using the Knights of Ren and trying to discover the mole among his ranks. At the end of the film it’s revealed Hux is the mole and is trying to get the galaxy to revolt against Ren’s empire and believes he can claim the throne after the fallout.
Many Force users have sought out Rey for protection, both really young and really old.
Rey and Kylo still converse through the force and can even manifest their whole presence in front of each other. It is slowly revealed they secretly love each other.
The big reveal in the film is that one of Rey’s “students” is actually her child, and Kylo becomes so enraged upon finding this that he nearly kills Rey who is only saved last minute by Leia.
[spoilers]How can the last bit of the B-plot happen? Carrie died before any filming on IX was done, unless they recast (which IMO would be highly controversial considering how beloved Carrie was) or CGI her like they did with Cushing, which is also risky.[/spoilers]