Well, repurposing footage from 7/8 was one of the prevailing theories for how they would handle this, and Disney only technically said they wouldn’t use cgi (a statement no doubt brought on by Rogue One having just been released the week before Carrie’s death).
Trevorrow said he wants to shoot IX entirely in 65mm, just as he did with parts of Jurassic World. I wonder if he’ll go through with it now that footage shot in a different format has to match with the rest of the movie.