Is an expiatory offering (kaffarat yamin) required of someone who swore not to acknowledge a person if specific information was not provided by a certain time, then agreed with that person to provide the information, but communication was severed before that due to unforeseen circumstances?

If you swore not to know your colleague after a certain time because he did not give you information, and then the electricity was cut off preventing you from doing so, you are not considered to have broken your oath unless you actually did what you swore to do. If your intention in setting a time was to urge your friend and show your concern, then do not break your oath. However, if it was for another purpose, or you had no specific intention, and you did what you swore to do, then you have broken your oath because the power outage is a common obstacle that occurred after the oath.

If your intention was to abandon your friend, this is not permissible, and you must break your oath and offer expiation. However, if your intention was not to befriend him, and he is a good person, then it is better for you to break your oath and offer expiation, for the Prophet, peace and blessings be upon him, said: "Whoever takes an oath and then sees something better than it, let him do that which is better and offer expiation for his oath."