Is it obligatory to fast to atone for an oath for someone who swore to visit a person on another day but was unable to fulfill his oath after traveling abroad?

If you swore to visit your friend at a specific time, whether explicitly by word, intention, or circumstantial evidence, and that time passed without the visit, then you have broken your oath (hanat) and an expiation for the oath (kaffarat yamin (definition)) is incumbent upon you. However, if the visit was not specified by a time, then you have not broken your oath as long as the visit is still possible. But if it becomes definitively impossible or highly probable that it is impossible, then the oath is broken at that point. The expiation for an oath cannot be fulfilled by fasting unless one is unable to feed ten poor people, or clothe them, or free a believing slave.