Since I first picked up Lydia (from Whiterun) as a “follower” I have been using her for most of the time. Yesterday I decided to use Benor (from Morthal).
During the entire time I have been using Lydia I noticed that she doesn’t really die. She just gets knocked out. Today I downloaded Dawnguard and decided to test out Benor. Without giving away any “spoilers” I can only say he didn’t last 5 minutes. He got destroyed so fast it almost felt pointless to even take him. With that I went back and checked his settings through the “Skyrim Creation Kit” and found he and Lydia are set up the same. However, as I mentioned, Lydia does not die, but Benor does. What do I need to do to keep him from dropping dead all the time? Also, Benor will not accept the "resurrect" command through the console.
Just a side note: I am quite familiar with the creation kit, I just don’t understand why the differences with the same settings.

I don't have Dawnguard so I can't check, but is he set to Essential or Protected? You can set those properties with the console command:

SetEssential <1/0> Set a character (NPC) as immortal (1) or mortal (0).

From: http://www.uesp.net/wiki/Skyrim:Console

Currently he set for Essential. So is Lydia. This is what I don't understand. He dies, and Lydia doesn't.

Maybe check in-game and see if it is still set? Otherwise, maybe it's just bugged...

I set him to be essential and he still dies. While I can set Lydia to protected and she won't die. I don't understand what is going on here at all. Maybe it is bugged, idk.