Ego Death

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Wikipedia defines ego death as a "complete loss of subjective self-identity". The term has multiple related, but distinct meanings, both in and outside of the plural community. The most common is "a headmate that ceases to exist prior to the death of the body".

This is, for obvious reasons, a touchy subject in the plural community. For some systems, ego deaths might be treated identically to the death of a friend or loved one. For other systems, they might be treated as nonevents. Or somewhere in between.

Obviously, every situation is different, even for the same system. Details such as the level of sentience, the age, the (mental) health, and the intention of the headmate might all play a role in how other headmates feel about the event.

Related Terms
Egocide:

walk out:

fade out:

Egocide is a term, seen as early as 2013 in the Tulpamancy community, that refers to Ego Death 'suicides' where a headmate becomes impossible to contact after severe depression. Generally, these are very emotional events for the rest of the system. This is not generally used for one headmate forcefully destroying another.

Walk out refers to a headmate leaving suddenly, but not necessarily in a negative way.

Fade out refers to a headmate slowly becoming more diffuse, absent more often, or otherwise more difficult for their headmates to contact. Similar to walk out, does not necessarily imply this is a problem.

Merging refers to two or more headmates or fragments blurring together in a permanent way, such that they are no longer meaningfully distinct. Some systems treat this as the ego death of the components, while others see this as unrelated to ego death entirely, or somewhere in between.