Tafsir of An-Nazi'at 79:39

"For indeed, Hell, whose affair has been mentioned, is the refuge." That is, his refuge, according to the view of the Kufans—that the al (definite article) in such a case is a substitute for the genitive pronoun, through which the connection is established. Or, it is "the refuge for him" according to the view of the Basrans, who do not consider it a substitute or a connector. This omission here is due to the knowledge that the transgressor is the possessor of the refuge, and its beauty is enhanced by "al-ma'wa" (the refuge) being a verse-ending (fasilah). This is what al-Zamakhshari chose.

The word "hiya" (she/it) is either a pronoun of separation (damir fasl) having no place in inflection, or it is a pronoun referring to Hell, acting as the subject (mubtada'). The statement indicates exclusivity; that is, as if it were said: "For indeed, Hell is his refuge, or the refuge for him, and he has no refuge other than it."