James will show up as a main character in the final book.
It would fit a pattern of the original three main characters. Quentin Jumped at the Call
, Julia on the other hand got put on hold.
That means the Call will hunt James down.
This will also fit with the series theme regarding how humans deal psychologically with magic. There's a very strong implication that people who are most capable of getting access to magic, are the people who are the least capable of dealing with it realistically (ie Julia failed her exam mainly because she was too dumbfounded by the existence of magic to concentrate, Quentin passed because he already kind of believed in it anyway).