I'm ready to get on the ship to go to Kara-Tur with Yoshimo and Kachiko, but after a bit of dialogue with Saemon Kachiko, Viconia and Hrothgar protesting that Leina (who is in my party) is still out there the conversation ends (regardless of what I say). Talking to Saemon starts the conversation over at the beginning. Are there Leina quests I need to do before I leave (I ran into Bjorn outside the Five Flagons and told him off), or is this a glitch?

Well, I did a full uninstall and reinstall, and the problem persists. Are there more things to do with Leina before I can leave, or is there something I can edit to make the problem go away (global variables, etc)?

NeJ2 Part 2 ends when you return to Ulcaster, talk with Tilorn and meet three orcs. It is the beginning of Dar's quest and end of the second part of NeJ2. We didn't investigate effects of NeJ2 on the overall game if you continue further without installing the third part which we're working on. I would expect from players and I've posted this already that you make a critical save before final dialogue with Tilorn and leave this game and/or installation for a while. But if you wish you may test what happens. Possibly I've already introduced the blank state in Leina's dialogue before leaving for Brynnlaw, but it has never been written and tested.

Is Hrothgar's presence required for the Dar quest? If not, I'll swap him for Dar and finish that quest, then try to leave again. If I still can't leave, I'll remove the Leina quest global variable in my save game, and see if I can leave then. I'll report what works.

It doesn't matter what variable you remove and what you do - there is no continuation of the story for now, there are no scripts, no dialogues, nothing... You may try to continue with the same characters but they'll be silent, and sometimes they may cause problems. If you wish to continue playing TS, I would suggest to remove them all as they are active only in NeJ2. Dar's quest is accepted in the end of the second part, but it has not been scripted yet, so you'll be able to continue it only in the third part.