So, Benor died. I know I'm responsible, but I don't really know how it happened. I wasn't using AOE spells (only one I had was Flamebolt). So here's what happened:
I received a bounty to kill a giant. My character is not the ideal build for such an endeavor (one handed, a bit of destruction, restoration, etc.) but I had just gotten the Animal Allegiance shout, and thought to myself - I'll get the Mammoths to fight for me... But instead they kept fight Benor (my adorably dumb follower from forever). I get distracted because I'm getting pummeled by a giant... The mammoths aren't really helping me out. I'm running, casting flamebolt, running more. Finally kill the giant, but I had run quite a ways. Benor is nowhere to be found. I run back to the camp, get the chest of loot, find a nice battle ax that I want to give Benny... Still hasn't caught up with me. So I fast travel to my current location. No Benny.

I find him crumpled near the corpse of the mammoth I tried my AA shout on. So, here's my question: I know that for the most part, the PC is the only one that can kill a follower, barring AOE spells cast by others/dragon breath weapons. Since I wasn't using AOE spells, and the only shout I used was AA, can that result in the death of a follower? Thoughts?

I'm not really sure but the only reason I could see this happening is that when the Mammoths join your side they gain the privilege to kill your follower as they are allied with you haha Also, as your follower was attacking the giant, they will attack him as they are not allied to him so will still kill him.

So, giants can kill a follower? They won't just ignore them once they take knee?