Aka, Is the room actually empty though?
As a GM, you will find that no matter how much you tend to prepare and how well you manage to recollect every rehearsed dialogue and hints for your players to react to, there will be points in your game where you find yourself ill prepared for a situation. Why? Easy.
Because there are players involved in your perfectly crafted world.
(And honestly, over-prepping only leads to headaches and railroading, avoid it!)
Players tend to walk off the carefully placed path you’ve set out for them. They will miss hints and obvious (to yourself, perhaps) elements of your story in order to progress.
In which case, they will start to think outside the box and ‘mill around’, trying to find things to either progress the story, or line their own filthy, near bottomless pockets. (Bag of holding anyone?)
Hence, there will always be moments where you must improvise.