For more than a century, scholars and Pagans (who are sometimes the same people) have debated the persistence — or not — of Pagan ideas and practices into the Chritian era. This is the question that Robin Douglas and Francis Young examine in Paganism Persisting: A History of European Paganisms since Antiquity.
Reviewer Ethan Doyle White writes in Reading Religion:

“Trying to escape the binary between the “hermeneutic of survival” and the “hermeneutic of concoction” that have historically dominated discussions on the topic, Douglas and Young outline a ‘hermeneutic of persistence,’ maintaining that “elements of paganism continued to exist in post-classical European society, constantly ready to be revived and reanimated” (2). Even while pre-Christian religions themselves essentially became extinct in most of Europe, images and ideas from those traditions persevered, allowing them to be adopted and reutilized by later individuals, some of whom considered themselves Christian, and others who were actively seeking replacements for Christianity.”
Get your library to order it or buy some expensive English electrons.