But and if she depart (εαν δε κα χωρισθη). Third class condition, undetermined. If, in spite of Christ's clear prohibition, she get separated (ingressive passive subjunctive), let her remain unmarried (μενετω αγαμος). Paul here makes no allowance for remarriage of the innocent party as Jesus does by implication.

Or else be reconciled to her husband (η τω ανδρ καταλλαγητω). Second aorist (ingressive) passive imperative of καταλλασσω, old compound verb to exchange coins as of equal value, to reconcile. One of Paul's great words for reconciliation with God (2 Corinthians 5:18-20; Romans 5:10). Διαλλασσω (Matthew 5:24 which see) was more common in the older Greek, but καταλλασσω in the later. The difference in idea is very slight, δια- accents notion of exchange, κατ- the perfective idea (complete reconciliation). Dative of personal interest is the case of ανδρ. This sentence is a parenthesis between the two infinitives χωρισθηνα and αφιενα (both indirect commands after παραγγελλω).

And that the husband leave not his wife (κα ανδρα μη αφιενα). This is also part of the Lord's command (Mark 10:11). Απολυω occurs in Mark of the husband's act and αφιενα here, both meaning to send away. Bengel actually stresses the difference between χωρισθηνα of the woman as like separatur in Latin and calls the wife "pars ignobilior" and the husband "nobilior." I doubt if Paul would stand for that extreme.