Ketubot, Chapter Four, Mishnah Eight
This mishnah discusses a husbands responsibility to ransom his wife if she is taken captive.
If he did not write for her, if you are taken captive I will ransom you and take you again as my wife, or in the case of a priests wife, I will restore you to your people, he is liable [to carry out these obligations], because it is a condition laid down by court.
One of the basic rights guaranteed in the ketubah is that a husband will pay a ransom for his wife, should she be taken captive. Even if this clause is not written into the ketubah, the husband is still liable, for it is a court-established condition.
As we learned in chapter two, if a woman is captured there is an assumption that she was raped by her captors, who are assumedly not Jews. Sexual relations with a non-Jew renders a woman forbidden to marry a priest. Therefore if this woman was married to a priest he must still pay her ransom, but he doesnt return her to being his wife. If she was married to an Israelite, she may return to him in any case.