Without knowing more, any answer is speculation.
How old was the hive cut out? Was their young enough brood in the comb saved to make a new queen if something happened to the old queen? How far away from the old hive location is the new hive located? Many variables.
When I've had bees disappear as described, the hive was queenless. Either she wasn't obtained in the cut out process, was damaged or killed during the process, or didn't appreciate the new home provided and absconded. If it was a young hive, it may have been headed by a virgin and there may not have been any brood in the comb saved. Sometimes the bees follow her when she attempts to make her mating flight.
If there wasn't any young brood or eggs in the comb saved, and the queen is MIA, then sometimes the foragers will simply find a neighboring hive to put their efforts into.
Any time I do a cut out on a young hive I add a frame of young brood to anchor them to the new box and assure they have something to work with if something happens to the queen.
Calm bees don't mean they are queen rite.
Depending on the numbers of whats left, you may be better off merging them with one of your current hives. If they're calm and few, a queen search should be fairly easy before the final decision is made.
Is whats left worth the time required to save it this time of year. Can they be built up enough to survive your winter?? How much brood and bees can my other hives spare to assist without effecting my fall honey flow?
These are questions you will have to decide for your operation.
For us, the question I would ask is "Can what's left over make a decent queen if I provide them a frame of young brood?" Otherwise I would merge them so they can be an asset to another hive.