With filming having not yet started on the final episode of the new Star Wars trilogy, we have little idea where the new movie will go. The Last Jedi surprised a lot of people, for good and ill, and that means that predicting what will happen with Episode IX is likely a fool's errand. Having said that, the one thing we do know about the final part of this trilogy tells us all we may need to know to guess how the new film will open. It will probably open with a funeral: the funeral of General Leia Organa.
One way or another, we know that the loss of Carrie Fisher will need to be dealt with in the story. She completed her work on Star Wars: The Last Jedi, but passed away before anything could be done with Episode IX. While Carrie Fisher is gone, General Leia is alive on board the Millennium Falcon with what remains of the Resistance at the end of The Last Jedi. There are numerous ways this could be handled, but opening the film with the funeral allows for the story to deal with what it needs to and provide the audience the catharsis it will need before the rest of the movie gets going.
Star Wars: The Last Jedi opened meer moments after The Force Awakens had ended, but that was an unusual move for the franchise. We're used to seeing years pass between episodes. In these gaps, while perhaps nothing major has taken place in the grander story, a great deal has changed for the characters. The rebels have been on the run, the Clone Wars have raged across the galaxy, etc. I would expect that Episode IX will go back to this practice and begin several years after The Last Jedi. The opening crawl will tell us that the story of how Luke Skywalker's battle with Kylo Ren has inspired many throughout the galaxy. This has, in turn, led to a resurgence of support for the Resistance. However, nothing has united so many people as when they came together to pay their respects to a lost friend.
Star Wars: Episode IX could take Leia away during this gap between the films, literally writing off her death in the opening crawl. Alternatively, it could see her die off-screen at some point in the film. Or perhaps she could even survive the film, but spend the entire story away from the main action for some reason. The problem is that any of these solutions would feel anticlimactic. There needs to be a moment where the audience gets to say goodbye. It's something they need. If you don't do it at the beginning of the film, the fans will spend the entire movie distracted waiting for what they know is coming to finally happen.
By making Leia's funeral the opening scene, Star Wars Episode IX will deal with this unfortunate necessity early, which means the viewers will be ready to move on once it has happened. In addition, it has the potential to act as a unique catalyst for the action. Recent rumors have indicated that Billy Dee Williams will make his return as Lando Calrissian in Episode IX, and what better way to bring Lando back into the story than by making him one of the people attending the funeral? Whether Williams' return is a cameo or a significant supporting role is unclear, but either way, if Lando is alive, would he miss Leia's funeral?
Exactly how Leia dies could also be of importance to the greater story. Perhaps she died at the hands of a new First Order weapon, because there will probably be a new First Order weapon. Maybe she was killed in a battle that will have other repercussions for the characters in the film. It's also possible (and it's the method that I would prefer) that Leia simply dies of natural causes after spending her life fighting for freedom in the galaxy. The fact that she passed away before seeing that freedom truly happen could be a major motivating factor for our younger generation of heroes to make sure that her dream becomes a reality.
I can't begin to guess where Star Wars: Episode IX will go as a story or what will happen to various characters along the way. However, the audience will walk into the theater wondering how one particular character will be handled, so it only makes sense that it be the first order of business after that opening text fades away.