If it's as simple as the AdBlue sensor not telling the computer that more AdBlue has been added to the tank, then yes, it would seem like a pretty simple fix. But it may not be that simple. If there's a blockage in the tank or the line that takes the AdBlue to the car's exhaust (where it's injected into the exhaust to reduce harmful tailpipe emissions) then the car may still 'think' that there's no AdBlue on board.

There could also be more to restarting an engine that has shut itself down than simply adding more AdBlue, too. Perhaps there's a specific restarting procedure that has to be followed, perhaps involving resetting the computer manually. One would imagine, however, that a dealership that sells the cars new would be aware of this.