Are monks allowed to travel during the rain retreat?

AFAIK, monks are not allowed to be away from their monasteries for more than 3 days during the rain season. But a monk I know had to travel out of the country due to some personal matter during this period for more than three days. So I'm curious to know whether there are specific situations in Vinaya where the monks are allowed to break this rule? If so, are they capable of receiving the Kathina robes?