Back around 2009 when they decided to jump ahead a hundred years in the continuity for the Legacy comics, I figured part of why they were doing it was to provide a huge empty space should a sequel trilogy happen someday. Meanwhile, they continued to write the ongoing adventures of Han, Luke and Leia in the novels.
They could've set Episode VII within the existing continuity if they'd wanted to. They didn't need to address much of what'd happened in the intervening 40 years, just that Chewie had died at some point, Luke was a widower with a son, Han and Leia had a daughter and granddaughter, etc.
I honestly believe they could've gotten away with picking up Episode VII at wherever the books were up to and still told a fresh, engaging and original story that would please the movie-only fans.
The simple answer to all of this is that Lucas never should've adopted the stance of "there is no Episode VII" because c'mon, how they hell else was this franchise ever gonna continue in any meaningful way? Yeah, there was the live-action tv series they dragged their feet on, but they were never gonna settle just for that.
What George could've (and probably should've) done is take a more supervisory role in the post-RotJ EU, saying "Maybe I'll make Episode VII someday, but in the meantime here's the history of what happened to our heroes after Endor."
Hell, I always assumed that keeping Han, Luke and Leia alive in the books was the contingency plan should Lucasfilm suddenly decide to make Episode VII.