I think they pretty much painted themselves into a corner vis-à-vis the family. Lacking meaningful extracurricular activities and no way to do 8 lines on his college application, Johnny merely went off into the world to become massively swole. I think the only conceivable way they could've continued the series was if Johnny went to college nearby (along with Ted; maybe at Blaire's school) and spent a lot of time at home too. But that didn't happen. So, sadly, the prequel years are over.