I have done all 3 excavations on this life and they were present in the journal. So as the wiki says, just abandon either the western or eastern excavation, do the 3 quests in that part again, then talk to Sal and choose "is there more to do here?", and he will send you to do the southern excavation....right? I have done this before and only needed to do re-complete 2/3 parts of the quest chain.
This time round I put up a LFM, 2 people joined, and one of them shared the eastern excavation. I clicked "yes" since I was planning to re-do that anyway. I completed the eastern excavation, talked to Sal, chose "Is there more to do here?", and instead of sending me to do the southern excavation, I suddenly had 3 "Quest reset" messages pop up and all the Threnal quests vanished from my journal.
Now, when I talk to Sal, he only has two options : Repeat the eastern excavation and "Is there more to do here?". If I chose the latter, he tells me they need time to finish shifting through the library and tells me to talk to the western excavation guy instead of sending me to the southern excavation. There are no Threnal quests in my journal however, not even the eastern excavation that I just completed a few minutes ago.
Not sure what happened here. Does sharing any of the Threnal quests cause the whole chain to break?
For those who are confused as to what the issue is, if you have already done all 3 parts, you can abandon either the western or eastern excavation, re-do whatever you abandoned, then go straight to the southern excavation. From the wiki : "Once the three are complete (be careful to not select the "repeat quests" option with Jal) go to Sal Danek and select the "Is there more to do here?" option. He will then send you to Zaveera Halfspear to complete the southern excavation chain. "