Does the mother's divorce take effect if the father swore an oath of divorce upon his son, to be divorced from her if he went to a certain place, and the son actually went there? And what is the ruling on this oath?

If the father swore by divorce [talaq] that his son would not go to a certain place, and the son went there, divorce occurs according to the majority of scholars, in contrast to Ibn Taymiyyah, who holds that expiation is required if the father did not intend divorce. The father must be informed of his breach [of the oath] so that he may take his wife back, provided the divorce has not become irreversible (threefold).