Board Thread:Skyrim/@comment-11344160-20140115023609/@comment-5046481-20140429170541

There are three status setting for NPC Characters, Normal, Protected and Essential. Normal dies when hit points reach Zero. Essential can’t be killed, they just take a knee for a bit while they recover. Protected (most followers and Housecarls) is in between and will take a knee when hit points are low sheding Aggro so they aren’t attacked while they recover. The player can kill them, but they can also die from the effects of Damage over Time (poison, bleed), and Area of Effect (Giant's tremor, dragon breath) or simple overwhelming force.

You can also use console commands to recreate an NPC or just make a clone. { player.placeatme 0001c1b9 1} will place a clone copy of Mirabelle Ervine at your location if you want to resurrect her after the College quest line is complete. YOu can find the REFID's of all the Followers and most npcs here in the wiki. You could also clone Uthgerd six times if you want. I made a clone of Annekke and she worked fine as a follower, even as a Steward, while the origional Annekke was home with Verner.