Basic structure to me seems to be X狂想曲はA鳴り響き、B根こそぎ壊し、鏖殺していく, a subject 狂想曲 with three verbals (X and A, B being their respective pre-noun and pre-verbal elements). 根こそぎ壊し、鏖殺していく seem to share the same pre-verbal as their object - "the people of the city"(?)).
What I don't understand is the bolded pre-verbal B. Why is it the postposition を used here instead of の?
NB**one could argue how far the adverbial 絶え間なく、かつ容赦なく applies but that seems to be ambiguous (?).