Is there an intention called "al-mufaraqah" (separation), and is it permissible for a traveler to cut short their prayer in congregation and pray alone with the intention of separation if they fear missing their means of transport?

It is permissible for a worshiper to separate from his imam if there is a legitimate excuse. This includes missing a train, which would result in significant hardship, or missing a travel group, the separation from which would cause harm. The Prophet, peace and blessings be upon him, did not order the man who prayed alone to repeat his prayer when Mu'adh prolonged his recitation. Similar excuses include hardship due to the imam's lengthy prayer, illness, fear of being overcome by drowsiness, something that would invalidate one's prayer, or fear of losing or damaging property.