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Halacha dictates that a man must hand the Get out of free will to his wife for a divorce to take effect.
If the man is mentally unstable, in a full time coma, a sadistic individual or his whereabouts are unknown the wife is essentially chained.
Is there anyway to circumvent this problem?
Recently read a case of Tzefat Bet Din granting a Get on behalf of a terminally comatose husband. I know the ruling is under scrutiny now by the Rabbinate. I don't know the details but it's a pretty well known case.