What should a husband do if his wife leaves without his knowledge and then informs him of this, knowing that it displeases him, and then she swore an oath of divorce, and the divorce occurred after 16 years of marriage, and she cares about nothing?

It is not permissible for the wife to leave her husband's home without his permission, except in cases of necessity. Otherwise, she would be considered defiant (nashiz) and disobedient to her Lord. If the wife leaves without your permission for no necessity and swears by divorce (i.e., makes a divorce vow), then what is commonly held as valid (al-mufta bihi) among us is that the divorce occurs if you have broken your divorce vow. If that divorce does not complete the three divorces, you can take her back during her waiting period ('iddah). If you did not intend to issue a divorce but rather intended affirmation, prevention, or encouragement, then no divorce occurs, and you are obligated to offer an expiation for an oath (kaffarat yamin). The matter should be addressed first with admonition, then by deserting her in bed, and if that does not work, then with a non-injurious beating.