The people on this forum have a real habit of not reading what other posters say.

1. Followers CAN die.

2. In most cases they WILL NOT die because they go into a recovery stance (enemies also go into this stance which frequently makes your Followers stop attacking them... I am tempted to say that this is actually a variation of the Shadow Warrior Perk)

3. If they are hit by ANYTHING, that does enough damage, while in recovery they will die.

4. If they are hit by friendly fire while in recovery they will die.

5. If they are hit by an enemy while in recovery they will die.

6. They can die from being hit so hard or fast by an enemy, or group of enemies, that they don't even go into recovery.

7. They can die from traps, especially the acid darts.

8. Any DoT that an enemy uses WILL kill a Follower.