I wouldn't give away adamantine for free. It's a major game-changer, I'd make it something they actively strive towards for a while. It's a 3000GP item, that's not spare change.
Rather, give them more consumable healing, buff and debuff resources. If they can keep the barbarian going (heal almost as fast as the gearsman pounds him) and slow down the gearsman with tanglefoot bags for example. That way they'll feel like they took it down primarily with their own strength and not with a magic button that you gave them.
Ah yeah that is a good point...If only they had went back to the room where Khonnir was held they could have had all of his stuff. That would have helped them a lot. But they didn't want to tango with the collector bot again,
My wife said that items found in a dungeon are not free, they are paid for in blood.
However, if Ascalaphus means that the party should not be given a 3,000 gp item in addition to the items already found in the module, my game replaced other expensive gear with the adamantine weapon. Page 17 in Fires of Creation describes a possible story award from Emelia Otterbie: four masterwork weapons. I asked about that award in this forum (link), because custom-made masterwork weapons would be finished well after the party would want them. Lord Fyre suggested substituting a single adamantine weapon.
I chose the wrong weapon for my substitution, an adamantine chakram made from an adamantine circular saw blade for a character who was trying to use chakrams but eventually gave up on them. An adamantine pick would be most believeable.
That would have been a great solution...if they had found him and informed Emelia. As soon as they attempted to rid the spores with fire and almost all got knocked out by the spreading, they haven't gone anywhere near that room.