Go back is to go to a place for the 2nd, 3rd, 4th, etc., time. A Comeback is the response to an insult. Insult: Your dumb! Comeback: Takes one to know one, poindexter!
It is in relation to the person speaking or writing. Come back means toward the speaker ( you have left his presence and need to return ) Go back means away from the speaker and towards your last...