On the other hand... there's a fanfic I'm reading where the author decided not to stop at the climax, and instead have a lengthy denouement.

Very, very lengthy. As in, three or four times as long as the original story. It's technically not a sequel?

But anyway, it doesn't have much conflict and what it does have is quickly resolved, with most of it being somewhat episodic slice of life. Maybe that's the kind of sequel you want?