This one was easily the most common method of departure for Companions in Classic Who. At the end of their last a story, a Companion would realise that they felt at home in the location of their latest adventure, and possibly find a purpose there such as the Fifth Doctors Companion Nyssa remaining on leper colony Terminus to help heal the sick. Claras history as a nanny and career as a teacher firmly establishes her as having a caring nature and loving children. Which definitely opens the door for her to leave the Doctor and start a new life caring for others like Nyssa, or some other purpose that she can turn her talents to. However, it has been the practice of New Who to establish companions with much more prominent home lives and families than in Classic Who. Particularly in the case of Clara who only travels with the Doctor occasionally while working full time, and having a family and a boyfriend. Although its not out of the question, Clara would be giving up a lot to stay in another time and place permanently.