The quest is finished. IMO the timing is quite unfortunate, it occurred on the night of a large update. Players who heard the announcement might thought the three were just lucky to be the first to encounter new content and clear it, when it had nothing to do with the update and was accomplished through meticulous planning and preparation.
With Wethermon put to rest, no one else would know how strong he was. It would probably be unthinkable IRL for an MMO to make content that can only be enjoyed by a single party, but that might be part of Shangri-la Frontier's Kamige appeal. I wonder if it has something else prepared (e.g. some kind of Shadow of Wethermon monster) for other players.
Curiously Rei was only worried about Pencilgon. Does she know Oikatzo's player is male?