The idea of returning to Earth had never crossed Khan's mind during that period. Nitis had left him in pain, broken, and cynical. Thinking hurt, which was why he decided to throw himself into a battlefield.
However, Lieutenant Unchai's words made sense on many levels. Khan was only seventeen. He was incredibly strong for his age, but he remained a first-level warrior with no deep knowledge. He was even quite ignorant about common subjects taught in the training camps.
An ambassador required far more than strength. Someone in that position needed a vast knowledge of the political array, multiple social skills, and a good understanding of alien's customs. Khan had nothing similar, but he was working on the last point.
It was clear that the path was long, and Khan understood how traveling through battlefields wouldn't give him what he needed. A peaceful period when he could study and fill his gaps appeared necessary, and Earth really sounded like his best option.