From Pluralpedia, the collaborative plurality dictionary
fading (v.)
Applies toheadmates

Fading occurs when a headmate starts feeling less present, may be active in the system less and less and eventually can leave the system entirely.

Fading may be traumatic to the remaining system members. In some cases, an entire system may fade, leaving only a singlet.

It is possible for faded headmates to return, as it is often extremely difficult to tell the difference between faded and dormant.