Why did my mercenary run away?

Yes, they can sometimes flee in the middle of a fight. It should be relatively rare, and the likelihood of it happening goes down as you purchase better mercenaries, but they do have an innate chance to decide, "This fight looks like certain death, I'm out of here!" and flee. This is called a "confidence level" and the likelihood of it happening also goes up depending upon the level of the foes, so a red-con mob has a greater chance to scare the mercenary than a green-con mob.

More information on confidence:

  • Confidence is based off of the con of the enemies, the number of enemies, and any mitigating effects placed on them (stun/root/mez/charm/fear).
  • The rating of an encounter is computed as a ratio of the number of group members vs. the number of enemies of even con. Enemies that are not of even con get counted for more or less than a single even con mob. Mitigating effects reduce the "enemy equivalents" an enemy is counted as.
  • In a group of two (you and your merc), apprentice mercs are balanced to get nervous with more than 2 even cons. Journeymen get nervous around 4 even cons.
  • The higher the tier of your merc, the less chance it has to lose confidence when the encounter rating is higher than its confidence. This is evaluated only when a new enemy adds to the encounter, and then it gives you 10 seconds to get the situation locked down before actually losing confidence.
  • Their chance to lose confidence is 25%, 20%, 15%, 10%, 5% respectively for tiers 1 through 5.
  • If a merc loses confidence it will be dropped to the bottom of any hate lists it is on (to avoid it dragging a bunch of mobs with it) and it runs a short distance.
  • Once it has lost confidence, it will re-evaluate the encounter every tick to see if it is confident again. Mitigating effects will come into play here if mobs can be locked down.
  • All in all, this is something that should be fairly rare and predictable for each grade and tier of merc.