Dungeon Hunter 5

The mission in question is mission 5, you are supposed to save some people. There are 2 groups, and one of the ones in the first group died while I was fighting an enemy, yet I still got the achievement. So, this achievement might be story related. The second group didn't have life bars that I could see, so I don't think you need to do anything special.

Let me know if you don't get the achievement (also note you can replay missions, so you can try again if this happens).