Does a divorce take place if a man says to his wife, "By the Haram (oath), if you do not return home at the specified time, then I will divorce you," and she does not return, and does he have to offer kaffarat al-zihar (expiation for zihar) if he takes her back?

The preponderant opinion among scholars is that prohibiting one's wife is a form of Dhihar. Therefore, what transpired from this marriage is considered Dhihar suspended on whether or not you divorce your wife if she does not return by the specified time. Consequently, you are faced with two options: either divorce your wife, in which case there is no Dhihar upon you, or refrain from her until you perform the Kaffarat al-Dhihar (expiation for Dhihar).