So, the book makes clear what happens when characters get 4 or 5 trauma (barely coherent and coma respectively). But what if toughened enemies get 1,2, or 3 trauma? I’m wondering how much they can take before running in terror? Or what other interesting effects may result? Ideas?
Toughened enemies can only suffer up to 2 Wounds and Trauma, not more. Only Nemeses can suffer 5 like player characters.
It really depends on the situation. Sometimes they will flee or give up if they have enough Wounds or Trauma.
As Shran mentioned, Toughened are taken out of action after two Harms of the same type. As with everyone, the first Wound (respectilvely Trauma) inflicts a +1 Difficulty penalty on all physical (mental) actions. However, it is up to you as a gamemaster to decide, based on the circumstances and in some cases player intent, what actually happens to the NPC. Of course, he might be dead, the canon provides a fair share of robust enemies slain by a killing strike of a certain Cimmerian but he can also be bleeding to death with a chance of healing, incapacitated (in the case of physical damage), driven irremediably mad, afflicted but able to recover given several months or just routed (for mental damage). I usually have this depend on what the last straw was, for instance a display of sorcerous might can have superstitious barbarians flee but awe scholars of the Dreaming West to the point that they lose themselves in half-remembered prayers to the Other Gods.
As a side note, you can also use these alternative effects on player-characters. While I recommend that you do so sparingly to avoid cheapening the sight of Harms accumulating, you can allow a player not to lose their character by having them left for dead on a battlefield or having recovered from insanity in a farm or convent of Mitra, conveniently coming back into action for the next adventure.
To add to what the above posters have said, if you’re worried about NPC’s “disappearing” once they’ve hit their max, you can use that as an indication to have the NPC leave the fight as soon as possible.
For example, a Toughened enemy with 2 wounds or 2 trauma is no longer in any shape to fight (but technically not “Dead”), so on their action they Withdraw or just run away. Imagine at 2 trauma a big brute realizing this wasn’t go to be as easy as his boss made it sound and all of a sudden not worth the money he was paid (or promised).
If any are left alive, you can use that as an excuse to bump up the number of enemies later in the adventure, if applicable (they managed to warn somebody).