So I finished the quest, talked to everyone, even did a sidequest, and then went on with the storyline. Many quests later I returned to Thirsk Mead Hall, just to see how it was going. I went inside and around 10 rieklings were inside. They attacked me. There was no trace of any of the people that helped retake it with me. When I went outside the people did spawn and helped me fend of the rieklings. This clearly was a bug because all rieklings had been killed by me before. Has anyone noticed this bug before?
Yeah, this seems to be a common glitch. Even after going ahead with the warriors of Thirsk Mead Hall, and clearing out the Rieklings, they do eventually respawn. This might be a coding error, and the Mead Hall itself may be considered a dungeon where by it's original inhabitants continuously respawn.