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:
So all we'd have to do is throw a blanket over her and ignore her? Works for me.
I feel like that is exactly what they did a few months ago.