The subject of Aguna, the stranded woman, is one of the most difficult subjects in Judaism. We are speaking primarily of a woman whose husband has gone overseas and has not returned for a long time.
On the one hand, the Rabbis feel for the עגונה, and will be more lenient with her than in other cases. For example, if one witness testifies that her husband has died, the Rabbis will free her to remarry without a second witness.
This special permission comes with a warning. Despite the Beit Din's permission, in the event that the testimony about her husband proves incorrect, and her original husband appears after many years, she is in big trouble. If she remarried, that marriage is canceled and her children from that second marriage are considered Mamzeirim. This marriage is voided retroactively and she must get a divorce from both husbands.
This is a very sensitive and potentially painful subject.
Rav Ovadia Yosef, זצ״ל, dealt with 950 Aguna cases during the Yom Kippur War. He permitted all of these women to remarry and in all of the cases, he was correct. The 951st case was one that Rav Ovadia was troubled with and he did not permit the one to remarry. A short time after issuing his decision, the woman's husband was found healthy!
Often there are Mitzvot that are beyond our comprehension. But as much as we are required to have faith in Hashem, we are also supposed to have אמונת חכמים, faith in the Rabbis.