Well, it makes sense for them to do this regardless of what they end of choosing to do with Leia in the next two films. Even if they do decide to write her out of ep.IX and have her character die in ep.VIII, they’ll still have to add some CGI. They obviously didn’t shoot a death scene so they’d have to use CGI to put Leia into such a scene.

Getting the rights to her appearance is just good “insurance” at this point regardless of how they end up using it. It’s a tad hasty, yes, but Disney has a lot of money riding on this and not too much time to solve the problem. However ep.VIII doesn’t come out until roughly 11 months from now, and they’ll have even more time to plan ep.IX, so it’s not like won’t have time to monitor how the fans react to this.