The magic preserving the lich's body against the ravages of time weaken, usually causing the body to gradually deteriorate until only a skull or even a single skeletal hand remains; this advanced form of lich is known as a demilich. Despite its ruined body, a demilich is far from powerless; if disturbed, the skull will levitate and suck the souls from nearby living creatures.
Quoting from the DnD wiki:
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I feel like that is exactly what they did a few months ago.