Does anyone have a complete list of followers that are marked as essential?
I know about Mjoll, Derkeethus, the DB ones and Barbas. Are there any others?

Essential Followers:
- Mjoll The Lioness
- Derkeethus
- Dark Brotherhood Initiate(Male & Female)
- Cicero
- Barbas
- Brelyna Maryon
- Lydia

No, they can acutally die and to add to the list Serana who is perhaps the only useful companion IMO