Part of an answer I provided recently might be of value to you for this question:

One of the greatest misunderstanding of pre-conversion European belief systems is grounded on two misunderstandings. The first is that religions do not change. While religions grounded on a written text are tethered to a certain extent, even they change over time. Belief systems without a written text change radically over time.

The second misunderstanding is related to the first, but it specifically involves the anachronistic projection backward in time of an idea of what a religion is in the twenty-first century, applying that understanding of an institution onto a pre-conversion belief system. The result is to see that belief system in an epic struggle with Christianity for primacy, and it makes that belief system into something that is monolithic - singular in belief and practice.

In reality, pre-conversion belief systems were fluid and not monumental. Beliefs were certainly different from place to place, from generation to generation, and from person to person. Using the analogy of what folklorists observed working with pre-modern European informants and their attitudes toward the fairy faith, for example, beliefs could even change as a person became older. Belief systems were extremely difficult to define and describe when they lacked a rigid book and a central "government" - for lack of a better word (referring to the Vatican or similar patriarchal locations).

One of the challenges to answering your question specifically is "which pagans?" and during "what period?" Each circumstance was difference, and no circumstance had a consistent universal response on the part of the non-converted community to the monotheistic religion.

Many Romans viewed the Eastern mystery religions (and Christianity could be grouped loosely with these) as creepy cults that subverted good old-fashioned Roman values and society. This was in some ways analogous to the way many Americans view Jehovah Witnesses, Mormons, or Scientologists recognizing that every analogy is flawed and breaks down at some point.

Many Northern Europeans apparently viewed Christianity with a certain amount of curiosity and awe. Pre-conversion belief systems in a pre-literate society were vulnerable to conversion because they were not monolithic, they were amorphous, and they were open to the idea of another supernatural being existing and entering their world - what's one more, after all? There was certainly a point when some people would have viewed the new religion as a bit of a cancer since converts too often turned with hostility to the old ways, but this reaction was typically too late to stop the process of change. That said, whenever humanity is faced with change of any sort, the reaction against that change is "typically too late to stop the process."

Perhaps this isn't much of an answer, but it may give you some things to chew on. Others could certainly add other perspectives.