Does a divorce take effect if it is conditioned upon something that has not occurred, such as the husband saying to his wife, "If you have done that, then you are divorced," when she has not done what he accused her of?

As long as you did not intend to effect a divorce, but rather intended to make it conditional on something you did not do, then the divorce did not occur, and nothing is binding on you. Conditional divorce on a past event is valid, so if he said: "If the matter was contrary to what I said," and "the matter was contrary to it," his wife would be divorced. We advise avoiding swearing by divorce and caution against impulsiveness when angry, due to the Prophet's (peace be upon him) saying: "Do not get angry."