So originally I thought that Disney would want to go and re-shoot a bunch of EP8 to write Leia out and give her a proper send off. But with them so far into post production I can see now why they wouldn't. A SW podcast I listen too, yes I'm that nerdy, began discussing how they handle her death in EP9.
The overall feeling was that it would be real shitty to give her an off screen death. Some wanted a replacement actress to fill the role like they did for Dumbledor in HP and some even thought they should go the CGI route like they did in R1. It looks like they could be going the CGI route or maybe this is for future projects that involve a younger Leia. This could also be just a negotiation to keep using her likeness for future products. I've also been seeing rumors that Disney is going to make her an official Disney Princess.
The reason I had originally thought they were going to do re-shoots is because it's rumored that the film will have a funeral for Han and during it there is an attempt to kill Leia and as a result it she falls into a coma. I thought they'd go back and just kill her off then.