Q never left because Q never leaves. This board allows Q to post anomalously to steer board with complete and total plausible deniability.
I've always tried to explain Q as like how I saw 'True Detective' playing out on TV and in the fan discussions.
True that many of the fans are very perceptive, but I always felt like part of the production was their posting as fans unbelievably astute observations that further the plot of the show. The show by itself isn't near as good as the experience with the discussions, but there has never been any admission by the producers that they were seeding them.