Maybe have the Spared henchman have a text box or something about them recognizing you.
Also, didn't like in the old games how "knocking out" became a forever combat aggro thing. This should fade over time. In BG1 it sometimes resulted in needing to quickly exit a room when someone was knocked out. It also meant that if this happened inside an inn for story reasons, you could never go back to that inn, even weeks or months later, because you would instantly be in combat with the person who was knocked out, and you might kill them on accident before you even knew what was happening.