I've never tried to get my Companions killed, either, although I've lost a fair number of them to combat and one to nature. When they die, their gear goes into my stash.
Unlike many folks here, I've never hired a large crew to hunt down robbers or Njerp villages. In fact, I only really want them (one of them) to help me deal with the individual Njerp I run across in my general area. I just consider it necessary because they can, and do, find their way to my settlement. It's been a shock to me to look up from some activity near home and find a Njerp, or a robber gang, heading for me.
Anyway, after taking a few arrows in the back, and from the stories people have related of their experiences with Companion gangs, I usually won't hire a Companion that has a bow and arrows. However, since they often offer the arrows in trade, I sometimes trade for their arrows and THEN hire them.
When they leave your employ, Companions often have pathing problems. My last one such forced me to open a hole in my fence because he wouldn't climb over it. When they reach a river, they can take a long time crossing over it. I've had another just stand in the road for weeks, even though his village was close by. I thought he was a robber and finally hired a guy and went to confront him, only to find it was a previous hire.
This is NOT gospel, but, supposedly the weapon quality affects the amount of damage inflicted, so, presumably, the armor quality could affect the damage taken. Otoh, I've been one-shotted by an arrow through the eyehole of my Masterwork Iron Spectacle helm, so, 'put not your faith in the works of Man'...lol. It makes a difference, too, what weapon type is used against you. Dark green can change to a lesser color, depending on the damage type the weapon causes.
(Edit: I took a Companion into a grove next to a village and told him to fell trees. He walked right through the grove, ignoring all the trees, and was heading into the village, apparently to cross it and get to some spruce trees on the other border.)