Complex sentence: The surrendered Primordials were banished to the Hell known as Malfeas, the Demon City and its unfortunate inmates; they are half-remembered only as the Yozis: ill-understood and impersonal cosmic deities whose continued worship is reckoned among the highest of heresies.
Split into simpler sentences: The surrendered Primordials were banished to/became the Hell known as Malfeas, the Demon City. Now they are half-remembered only as the Yozis: ill-understood and impersonal cosmic deities whose continued worship is reckoned among the highest of heresies.