Current reports seem to suggest that the iconic actress had already finished her work on Episode VIII prior to passing away, which means that the Star Wars franchise may not have to completely cope with her death until production begins on Episode IX.
That leads us to believe that she may at least see Luke again by the time Episode VIII debuts.
As of right now there doesn’t appear to be a concrete plan in place for dealing with Fisher’s death, but there’s still time to figure to the logistics.
Looking to the future, the two clearest paths seem to be: write her out of the Star Wars universe or use CGI (like Rogue One did for Tarkin and 19-year-old Leia) to keep her around in some capacity.