I see this
site has a long description of things.
This is the final bit about destroying the thing.
Destroying the Orb:
The Death Orb can only be destroyed if all of its gems are properly inset. It must then be subjected to the following effects, in quick succession and in the proper order: a wind of 50 or more mph force; the strike of a maul made from a solid piece of granite; a very hot flame (1,000 degrees R); and immersion in very cold water (32 degrees F.). The procedure causes the Orb to shatter, which causes the Elemental Nodes and the Greater Temple (Dungeon Level Four, area 417) to collapse, and the dungeon levels above as well. Zuggtmoy takes 111 points of physical damage, is unable to use any powers for four days, and cannot leave her own Abyssal Plane for 40 years. luz, having less invested in the Death Orb, merely loses the services of evil elemental creatures for four years
Destroying the Orb takes half her HP. Yes. However, (1) then the party can't get back into her prison, and (2) the party won't know all the specific steps to destroy it, and (3) when the Orb is destroyed, so are the levels in the Temple, at least 3 & 4, so Zugg cannot be engaged after that. Am I misunderstanding something?
That text is taken directly from the module. It does not contain any info about how the Orb is used to defeat Zugg.