Ah, Hemeth. One of my favorite NPCs from OotA.
They met him in Sloobludop, of course, and he escaped with them and led them to Gracklstugh. Along the way, he revealed that he was a weapons smuggler, and offered to sell them quality Nephelium weapons from the secret stash in his boat (which was recovered from the docks in the scramble out of Sloobludop). This was to foreshadow the Gates of Firestorm Peak, which I used in between Act I and Act II of the book.
Hemeth left the party once they got to Gracklstugh, which they left in some amount of disarray. He popped up again later in the duergar outpost under Firestorm Peak, where he started calling them "bad coppers" for showing up again in his life, and grumbled about some of the madness that had followed their leaving Gracklstugh. If you know Gates of Firestorm Peak, then you know that the PCs can cause quite a bit of upheaval there as well, and mine did, assassinating a hated leader but getting "framed" by the very cleric who paid them to perform the assassination right after they had done the job. And shortly after they left the outpost, it was invaded by undead illithid accompanied by none other than Orcus (this was off screen).
Hemeth showed up again in Mantol-Derith (he IS a smuggler, after all). They met him with other duergar near the gates of the duergar compound, where he grudgingly warned his fellows that "these topsiders -- bad coppers all -- be right good in a fight". When the PCs were finished in Mantol-Derith, they left "the gem" there without realizing what it was (they turned it over to the duergar), and of course all Abyss broke loose there afterwards (again, this was off screen after they left).
Hemeth showed up AGAIN in Menzoberanzan, where the PC dwarf ran into him accidentally while he was negotiating a deal with a drow contact who was trying to purchase some nephilium. He took one look at the dwarf, cursed under his breath, and informed the drow that "tha deal be off", on account of "that softbeard (the hill dwarf) an' 'is bad copper friends" being loose in the city. He'd seen everything go to heck each and every time they'd shown up, from Sloobludop on, and had decided to get out of dodge at the first sign of them. Which was quite canny on his part, since it wasn't long after that that Vizeran summoned hundreds of demon lords to Menzoberanzan...