The Merman's Children, I have reached the passage where Pavle Subitje predicts the end of Faerie. I previously summarized this passage here and have just now added some explanatory links to that earlier post.
Are mythological beings literally driven out of existence or do they adapt and adopt new forms? And are they joined or challenged by new entities that are gods in all but name? See the link to "gods fiction" here.
From the empirical datum that gods are not or no longer overtly present on Earth, it may variously be inferred that they:
have ceased to exist;
have been superseded and replaced;
These inferences, except the first, generate alternative premises for modern fantasies. Poul Anderson, as ever, follows the implications of more than one premise.