I personally think it will be written in the opening scroll that the film will be taking a time jump hence she had passed away since it had been a few years since the events of The Last Jedi. Now that’s my Theory.
It’s already a known fact that Leia had a much bigger role in IX and since her passing Lucasfilm had to basically scratch her out and even confirming they would not bring her back in any CGI form.
With JJ Abrams recently finishing the script it pretty much comes down to him what sort of role her passing will have in the film. I mean leave it to JJ to find a way to make things right and somehow give her the peace she deserves.
Well in the new The Last Jedi novelization which is being released in a couple weeks, the book gives us a few hints that don’t bode well for the general but at the same time makes so much sense.
Everyone’s most hated scene in the film was hands down the Super-Leia scene where she floats in space after the destruction of her ship. It was the first time she uses the force and it came off a bit corny. I myself had no beef with it since you’ve never seen how strong the force truly is for her, so again I was fine with it.
In pages that have been leaked from the book, we find out that after waking from her coma, Leia is not well and still very much sick and is suffering from solar radiation and hypoxia.
This explains why she has her face covered when we next see her on Crait in the salt mine.
There’s a pretty great chance that she simply can’t survive such a traumatic event, which leads me to believe we might get a funeral scene after all in IX.
We’ll know more from the book when it releases on March 6th