Some companions lose their essential status when dismissed.If they're not healed within a set period of time, or when the player travels beyond a certain distance, they will leave and return to their last used home base. If one is playing in Survival mode, the companion must be healed when incapacitated, even after combat.If incapacitated, they will automatically heal after combat ends. Unlike Fallout 3, companions are marked as 'essential' when acting as active companions, meaning they cannot be killed.

The game has a number of temporary companions that will only be available during certain quests. Steal Owned Items (may upgrade to Hack or Lockpick)