It almost looks as if the adventuring fellow you get through the missions is an attempt to get rid of the shouting for a party aspect of missions. There are missions where your fellow will fight with you as long as nobody else is in your party. Maybe later you'll have 3 or 4 AI controlled NPCs with you helping you, but for every party member that you bring along, one of those NPCs wont do anything. So yeah, along those lines of not blocking anyone from getting the main storyline going solo. But also on that same coin, the missions will never be terribly difficult.