The oath and the laurel wreath will pop up again in the future, yes.
I struggle a bit to phrase this in a way that's neither a spoiler nor so short it's unsatisfactory, but what I can say is that the Ruthless Route reveals that there are important, worthwhile things to be done in the valley, from which Asterion stands to gain. Some of those things, however, may require him to be there to be accomplished, no one else can do them.
The Ruthless route shows one of those worthwhile things, but there are more. The valley has many secrets.