I'm only writing what I've read. Am I wrong?
I've been wrong before. It'd be nothing spectacular if I were incorrect. But I read all about this a few months ago when it was a major topic.
Admittedly, "haha what?" is a pretty unhelpful answer, but wikipedia (FWIW) lists pagan Roman emperors as late as the late 300s, and of course the famous conversion of Constantine the Great ... well, he wasn't emperor until after 300 AD. Justinian also famously shut down an Academy (established in the name of Plato and his philosophies and beliefs) -- that would have been in the early half of 500s AD. So, certainly not eliminated that early, but I haven't heard anyone proposing evidence that there should be any nobility/etc worshiping the old Hellenic gods by Charlemagne's time.