Sometimes they build a queen cell because they didn't like the disruption of moving and they blame it on the queen. Sometimes it's because the old queen is dead. Usually they build more than one. It's LIKELY there is another queen cell somewhere, but if there isn't and if there isn't a queen, then they may be hopelessly queenless now because the larvae may be all too old to make a queen. A frame of eggs and brood, if you can get one, could save them and you don't have to find a queen or a queen cell because it just gives them the resources if they need them.