What happens to the kingdoms represented by the image when the stone hits?
The stone strikes the image's metals from the feet up, and the kingdoms they represent are crushed, becoming like dust or chaff of a threshing floor blown away by the wind, leaving nothing. Then the stone becomes a kingdom filling the whole earth.
Les teaches that as Christ the stone smites all the metals that make up this image, beginning with the feet, they become like the dust or chaff of a threshing floor that the wind can just blow away. Everything those metals represent is blown away, with nothing left of it. Then the stone becomes a kingdom, and that kingdom is not confined to the land of Israel but fills the whole earth. This kingdom is spiritual, physical, and political, set up on the earth, with Christ as King of kings and Lord of lords over a kingdom of righteousness, holiness, and sinlessness, yet it remains the one and only kingdom.