I was able to following the imp hero right back to his spot beside the chieftain's house. I didn't get the automatic cutscene with him bragging (didn't try leaving and then returning), but could talk to him and send him back to his wife.
Once in the prison at the start of the act I talked to the chieftain's son with the door closed, and he ran around the room twice trying to leave, then faded out. AFAIK, there shouldn't be a problem in general with following NPCs.
