DO SO, that would be amazing and headcrabs are underpowered anyway. The main problem is that most ZS maps don't got NPC nodes (waypoints). There're no other ways for us to add them.
Headcrab went to headcrab heaven. We originally planned to make a headcrab npc which would spawn if you killed a zombie (without a headshot). We might do something with it in the future.
Oh you got the Steam version. Try to verify the cache (right mouse button > properties @ Steam) after deleting gta_sa.set (and make sure you delete .set and not the .exe in another folder!!).