They don;t have to give you notice that they are leaving - what you are worried about is a negative review. And they have not said that anyt of the reasons you have listed influenced their decision to leave.
On this occasion my strategy would be to leave it to the last minute to leave a simple but factual review sayinig that the guests were unfortunately uncomfortable in agreeing to local 'green' requirements.
YOu could, if you wish, email them now via the AirBnB platfrom to ask if everything is ok as there does not seem to be anyone at the property. (How did you fine this out - maybe they are using it as a base for other trvaels)