The sudden rush of wind had taken Robilar by surprise. His first thought was that it was some new form of attack the stalker was demonstrating. But no, he had felt the impact of his sword -- and he had killed enough beings to instinctively know when he had struck vitals.
The wind had bowled him over, but Robilar stood up and listened for a moment. The wind was gone. There was no movement. Robilar poked around at the ground in front of him with the sword. There was no invisible body, but he suspected the creature had simply dissipated, returning to its home plane, as some other outer-planar things had done upon his killing them.