In a 2008 interview with Total Film magazine:
TOTAL FILM: "Are you happy for new Star Wars tales to be told after you're gone?"
LUCAS: "I've left pretty explicit instructions for there not to be any more features. There will definitely be no Episodes VII-IX."
Well, once he's gone I don't think anything will stop the eventual sequels. It's not like the empire would suddenly crumble after the death of the emperor and vader.
Does he want lucas arts to just tell stories about the clone wars ad nauseum? If anything, the empire would be more interesting with power struggles now that the sith are gone.