The fact that Will slew an ancient evil dragon from the time of the gods, even before the High King ravaged Southmark is nothing short of a full-blown legend in itself. It's only right the townsfolk celebrate this possibly once-in-a-lifetime event: Valacirca could have easily been a threat to the world of humans if he wanted to be, and this definitely made the world at least a little safer for humanity. There's still the High King left to worry about in Southmark, but for the moment it is not yet time to face that threat. Our heroes deserve a little break.
Also, Anna and Reystov should marry ASAP... Now is exactly the time to get swept up in the festive mood and celebration. The heroes don't exactly have the luxury of time since the High King is still a looming threat, once his seal breaks which is likely a matter of when and not if.