Considering the feat does not work for Layonara, I do not think this is going to make things unbalance.
//please do note that the disarm feat does not work against monsters in Layo, just fyi.
Monsters cannot be disarmed; therefore, the Improved Disarm feat is not useful.
Orcs, skeletons, gnols, kobalts, goblins, sahuagin,
So the decision sounds like it's about NPCs not causing PCs to lose their weapon to an area clean-up script if the weapon hits the ground rather than a PC collecting +5 weapons in surplus, if I understand correctly.
Anyways... just the question is all I'm wandering now... would a disarmed NPC simply redraw there weapon or continue fighting without?