Ashton didn't stay at Sylvenvale despite the Guildmaster's convincing. Ashton was determined to fulfill his end of the bargain and nothing could change his mind, the Guildmaster knows that too.
And so, even though it pains him to see Ashton go, cause Sylvenvale would lose a fearsome protector, the guild master had no other choice than to let him go.
Of course, Ashton left something that would protect the city in his disappearance. He hopes that it'll never get to the point where that something get's triggered by another invasion, but at this point? Only time could tell.
After leaving Sylvenvale once more, Ashton traveled for almost a month and arrived at his next destination, which is the Forest of Hallucinations.
