Spoilers for those who haven't seen TLJ. (But if you haven't seen it why are you here? Go and see it).
After the sad passing away of Carrie Fisher it was always clear that The Last Jedi would be her last role as Princess/General Leia. The film ends with her alive. The last of the trio from the original trilogy. An odd situation when others are dead but the respective actors can return.
But the film hints that there could be a larger role for Leia in the next film. Each film till now had a larger focus on one character. Say The Force Awakens was of Han Solo. The Last Jedi could be said of Luke Skywalker. The next film might have been like that for Leia. Kylo's not killing her could have seen a big payoff.
But now it looks like the plans would be altered. What do the fans want? What do the fans think is best way to respect her?
Personally, i think it is best to recast her role. To say something like she died in between the films would be of a bad taste in my opinion.