From what I can remember they work like pets. Which means they have a damage reduction of 90% when getting hit by Aoe. A mob faceplanting them a couple of times killed them even in MoP. So that part hasn't changed
. So unless I'm mistaken or they have changed something, they must get hit by 1 hell of a aoe ability inorder for them to die. While writting this I was thinking about healers current state of Aoe healing, since our spirits will still need some healing when they do get hit by Aoe. Might just be a shot in the dark though.