Unfortunately, this is a very real halachic problem and one that is all to common.
Questions about missing husbands arose as a result of 9/11 when many many people were murdered while at work in the World Trade Center.
There are also the tragic cases of Tami Arad, and more recently Karnit Goldwasser, whose husbands (Ron and Udi) have been missing in action for many years (Ron Arad for over 20 years, Udi Goldwasser for over a year, may HaShem please bring them and the other MIAs home back to the families quickly and in good health).
There were also many questions by women who returned from the Ashes of Europe 60 years ago whose husband’s disappeared and whose fate was not known.
I once read (and I’m sorry I don’t remember where) that a way to view Jewish History, and assess the important issues of each generation is to look at the Shutim that were being asked or addressed by the G’dolim of that generation. If you look at Shutim in the second half of the Twentieth Century, particularly at Shutim by Rav Moshe Feinstein and Rav Shlomo Goren, you’ll see that the tragedy of Agunot is an issue which continues to trouble our nation well into the modern era.
One of the questions that came up in the Daf Yomi Shiur was why we don’t reinstate the Get al T’nai that David HaMelech had his soldiers sign before they went out to battle.
A get Al T’nai (as far as I understand) is basically a document that says that if a soldier does not return within a fixed period of time, this is to be considered a get retroactively, and the wife has the status of a divorcee and not an Aguna.
Had such a practice been in place in the IDF, this would have helped the plight of Tami and Kamit, not to mention the wives of the soldiers lost on the Dakar submarine, and many other cases of soldiers whose fate is unknown.
I vaguely remembered hearing that in the early days of the State there was a discussion about instituting a Get al T’nai, and with a little Internet research I found a reference to Meshiv Milchama, a book of Halachot for soldiers by Rav Goren where he discusses a proposal from Chief Rabbi Herzog to institute such a Get for all soldiers. Rabbi Goren actually drafted a Get al T’nai, but dropped the idea when commanders said that this proposal would be demoralizing for soldiers. I briefly looked for a copy of the book in the B’nai Torah Library, but didn’t find it.
It’d be interesting to read this source if/when I manage to locate a copy.
What surprised me more in my Internet search is that although it is not standard practice in the IDF today, there are many other modern examples of use of a Get Al T’nai.
The person sitting next to me at Daf Yomi on Sunday said that he actually had a Get Al T’nai that his wife’s grandfather wrote to his wife when he went to battle in World War 1.
According to the Jewish Virtual Library this get was used during the Russio-japanese war:
During the Russo-Japanese war of 1905, some great Russian rabbis visited the troops before they left for the front and persuaded the Jewish soldiers to issue a get al tenai, a "conditional divorce," so as to free their wives from the status of agunah should the men fail to return. But obviously this temporary procedure, however helpful in individual cases, did not meet the growing dimensions of the problem.
I also found this short description that claims that a Get Al T’nai is also used today in the IDF in certain cases, although I was unaware of this, and am not sure of the accuracy:
As there is conditional marriage, there is also an option of conditional divorce. According to Mishnah Gittin a man can give his wife a get and tell her that it would be valid in case of an adverse event such as: not returning from a trip, being declared missing in action during a war, loosing his mind and other exceptional cases. A different option is for a representative of the husband to write his wife a get if such an event occurs. At times, the rabbis took such initiative and suggested that a conditional get be written. In 1987 Israel extradited a Jew named William Nakash to France. Before he left the country, the Rabbinic Court in Jerusalem insisted that he deposit a conditional get with the court, which Nakash agreed to.
This solution, however, was only suggested in relation to soldiers going off to war. According to Halakhah, it is not possible to give a conditional get once and to keep it until it is needed. If a man goes to war, gives his wife a conditional get, then comes home on vacation and is intimate with her before returning to war, he must give her a new get. This means that a new conditional get must be deposited each time. The IDF (Israeli Defense Forces) has a conditional get version that can be deposited before a particularly dangerous mission.
The above was certainly news to me, I had always thought that the concept of "get Al T'nai" had not been used since King David's army - I guess that you learn something every day.