The expedition included Roots, From-Deepest-Fathoms, Breya and Drennen. During the expedition, he was killed after he ignored Breya's warning that "something doesn't feel right" and walked right into a booby trap.
His corpse can be found just outside Avanchnzel Boilery, shortly after a swinging blade booby trap, which may have been what killed him. His ghost can be seen throughout the ruins, musing over the Dwemer technologies. He seemed to covet the Lexicon for himself.
Drennen "I don't like this place. It feels like we're being...watched."
Breya "Its a simple job, Drennen. We get in, we steal the Lexicon, we leave. Don't get jumpy."
Fathoms "If you two cannot handle this, we can find others to hire."
Roots "Enough. Their services will be more than adequate. Let us continue."
Drennen "This place is unbelievable."
Roots "Indeed. Avanchnzel is as much a library as it is a city. Built to hold the vast memories of the Dwemer."
Breya "Why are all these...things...ignoring us?"
Roots "Avanchnzel is waiting."
Breya "Waiting for what?"
Roots "No one seems to know. Perhaps the return of the Dwemer. Perhaps the ending of the world."
Breya "Best get rid of the ones we see. Just in case."
Drennen "This place is huge."
Roots "It is large, indeed. I did not anticipate Avanchnzel's size or the time needed to uncover the entrance. A few hours sleep and we should be ready to continue through."
Drennen "Maybe we should turn back. I don't want to sleep here."
Roots "Drennen, do you understand that the Lexicon at the bottom of this place holds the accumulated memories of centuries of Dwemer."
Breya "Not to mention our pay."
Fathoms "So we're not turning back, you fool."
Breya "Besides, you're not afraid of a few sleeping metal men. Are you, Drennen?"
Breya "I thought you said these things were 'sleeping'?"
Roots "You said they were sleeping. I said they were waiting. It seems a few of them were 'waiting' for someone to try and take the Lexicon."
Drennen "I can't do this. We shouldn't be here. I'm sorry."
Fathoms "Let the field mouse run. Your pay will be double."
Breya "My pay will be nothing if we die in here!"
Roots "Calm yourself, Breya. We are close to the Lexicon. I can feel it calling. We can do it without Drennen."
Roots "We are close now. Can you feel the Lexicon calling out?"
Fathoms "[sarcastic] Sure."
Breya "So we get it and get out, right?"
Roots "Once we have the Lexicon, we need to take it to its podium. I know what to do from there. Soon the Lexicon's knowledge will be mine."
Fathoms "Ours. Soon the Lexicon's knowledge will be ours."
Roots "Of course."
Roots "We're almost there. I can hear the Lexicon. Come on, quickly!"
Breya "Something doesn't feel right. [pause] Wait!"
- His name is shortened to "Roots" in subtitles, likely because his full name is too long. "From-Deepest Fathoms" is also shortened to "Fathom" for the same reason.