Halakhah su Levitico 18:18

A husband whose wife disappears may not remarry without proof of her death. We are much more lenient, however, for men whose wives disappear, as the prohibition for a married man to marry a second wife is only rabbinic in nature, whereas the prohibition for a married woman to marry another man involves a capital Biblical offense (see Pitchei Teshuvah, Even Ha’ezer 1:14). Rav Yonah Reiss,³Citations of Rav Reiss throughout this chapter come from two lectures that I heard him deliver, as well as personal conversations. Director of the Beth Din of America, informed me that a number of husbands called the Beth Din of America after their wives disappeared in the World Trade Center attacks. Rav Reiss said that the Beth Din followed the view of the Gesher Hachaim (1:19 note 4), who rules that a husband may remarry if adequate evidence exists that his wife was at the place where a tragedy occurred, and that most people who were in her location and situation perished.⁴See Teshuvot Minchat Yitzchak (1:6) regarding the necessary level of evidence in order to permit a man to marry his wife’s sister during her lifetime, a Biblical prohibition (Vayikra 18:18).

The nakedness of a woman and her sister: To not have intercourse with two sisters, meaning to say that a man not marry two sisters together - and not even this one after that one - during the lifetime of the first one; and even if he divorced the first one, as it is stated (Leviticus 18:18), "And a woman upon her sister shall you not take to be a rival, to reveal her nakedness upon her during her life." The explanation is a woman and her sister together, "shall you not take to be a rival," [which] is an expression of rivalry - meaning to say that he should not make one the rival of her friend; "during her life" comes to teach that even [if] he divorced the first, he shall not marry her sister - and that is [the meaning of] the expression, "during her life," meaning to say all the time that she is alive. But after the death of one, there is no doubt that it is permitted to marry the other. And that is what the verse stated, "during her life." And likewise, if he lays in the way of licentiousness with the sister after he married the first one or designated her, is also included in the prohibition; as the Torah was concerned about the the marriage of [only] the first one.