In The Sims 4: Realm of Magic, although spellcasters aren't immortal, they can brew a potion of immortality which only spellcasters can create.

In The Sims 4: Vampires, much like in The Sims 2: Nightlife, vampires stop aging once they become a young adult.

Ghosts remain immortal, but can be killed if they are revived first.

This effectively renders them immortal, as the people who are instantly revived in the case of an accidental death lose the ability to die naturally.

Though a trait and not a life state, Sims with the Unlucky trait cannot die of anything other than old age (the Grim Reaper will immediately resurrect them due to their death being too amusing and predictable), but if they drink the Age Freeze potion or have the Immortal Lifetime reward, they become ageless and lose the ability to die from old age.

In The Sims 3: Into the Future, Plumbots, much like Servos, cannot die of old age and can only be killed by a falling meteor, although some store items such as the Cowplant or the Door of Life And Death are capable of killing Plumbots.

In The Sims 3: Late Night, while still possessing greatly augmented lifespans, vampires are no longer immortal and can die of old age, although if The Sims 3: Supernatural is installed they can acquire the Immortal lifetime reward to make them completely ageless and immune to the sunlight.

Much like in the previous two Sims games, ghosts are still essentially immortal, although they can be permanently removed from the game if their tombstone is deleted or they are made playable and choose to Return to the Netherworld.

In The Sims 2: Open for Business, Servos do not age, and can only be killed by a falling satellite, being eaten by the Cowplant, or by running with scissors.

In The Sims 2: Nightlife, vampires, much like zombies, cannot age, although they can be killed by other means, notably their vulnerability to sunlight.

In The Sims 2: University, zombies are unable to age past the Adult life stage, and therefore possess the potential to 'live' forever.

As in The Sims ghosts cannot be killed, as they are already dead.

Most NPCs, such as the firefighter, cannot be killed.

Ghosts cannot be killed, as they are already dead.

There are many life states throughout the series which are inherently immortal, and possess the capability to live forever unless killed through unnatural means. Various life states throughout The Sims series possess this ability, and multiple methods exist to achieve immortality. Immortality is the ability to live forever or avoid permanent death, either due to inherent abilities or use of external methods to prolong one's life indefinitely.

Sims 4 become a vampire