The Safed Rabbinical Court recently gave a woman a "get zikui" to permit her to receive a divorce from her husband who has been in a coma for seven years. See this article. The article describes it as "rare." What exactly is a get zikui and are there any recorded instances of it being used recently?
Rabbi Isaac Herczog discussed the concept, and rejected it. (Rabbi Hershel Schachter has discussed this in several lectures.)
"Zikui" works as follows. I want to gift someone a nice challah knife on shabbos, but it's best to avoid gifts on shabbos as it looks like a business transaction, so on Friday afternoon I say, "I'm sure Shmerel would want to receive this lovely challah knife, so I'll have my friend here pick it up on his behalf." Receiving on someone's behalf, when we assume they would like to receive it, is zikui. Another example would be if I set aside food in my apartment building for anyone in the building to use on shabbos -- this makes an eruv and allows everyone to carry. If I can't contact Shmerel in advance, I can generally assume "he'd like to be able to carry", and thus have him receive a share in this food.
The argument used here was: "he would want his wife to be free if she was chained to a vegetable for six years." (Or a similar argument, "he disappeared off at war; if he's still alive in some Hezbullah prison three years later, he would want his wife to be free now.") Herczog correctly predicted that if we allowed it for the husband who's disappeared, some rabbi would try this stunt for the husband who is right here and refusing to give his wife a Get, arguing that he'd really rather give one. (And as Rabbi Schachter tells it, sure enough, some "rabbi" started doing such Gittin in Israel -- he's unauthorized by the Israeli rabbinate and therefore could be arrested for this, so he does them at the US Embassy.)
As Rabbi Schachter explained, the fundamental problem with zikui is that it only works (at least in all the Talmudic precedents) in a passive way, to receive something. Giving a Get requires some very deliberate action.
The story of the vegetative husband (or similarly, one stricken with a severe psychological or neurological problem to the point he can't execute a Get) is truly tragic, but the halachic logic here seems shaky at best.