Related על כתובות 102:10

If [a wife] is captured, he is not required to redeem her. When does this apply? When she is a captive of the government, but if she is a captive of bandits he redeems her—if he wants to uphold it he can [and pay the bandits to redeem her], or else he divorces her and gives her a ketubah of 100 zuz. If she is captured after the death of her husband, her levirs are not required to redeem her. And that's not all—even if she were captured while her husband was alive and after that he died, the levirs are not required to redeem her.