Reading the script I do believe you could probably have accounted for Fisher’s absence by using the film’s time jump to have her die between movies, and then split her storytelling duties here between other characters. Have her military duties handled by Connix, and then have the familial/Force duties handled by… Anakin. Honestly, his effect on Kylo probably would be more meaningful as he’s written than Leia’s since Anakin is who he looks up to, Anakin’s the only person in the world who has ever been where he is, and Anakin’s the only person who can explain to him why it’s better to do good while you can before you go.
Plus, having the film stop for a second after the first act to recognize Leia’s absence through a resistance memorial somewhere on the compound that the characters meet at would have been a much better tribute to the character than the weird semi-resurrection they gave her in TROS. Plus having Fisher’s real-life daughter assume the duties of Fisher’s best known character, but with Lourde’s character instead, seems more in keeping with how this trilogy works.
Alternatively, you could have ROSE be the new Resistance leader in that case, but I feel that probably takes her out of the action too much and I like the way she’s used here.
To the idea that they should have pushed this back a year - they probably could have developed this in the time they gave it just fine, if they hadn’t been so insistent on specific beats being hit. If they were actually going to push it back a year, my feeling is they’d have done that, and then just gotten Rian Johnson back. But then again - who’s to say they wouldn’t have tried the same thing with him that they did with Trevorrow, now that they’re developing THE END instead of just a Part 2.