So I had just had my bard dominate Otis, and as we walked out of his shop he said he had done all he could or something like that and just walked away. I even had Elmo in the group! I'm guessing this has something to do with Otis's hard coded programming but dang.. what an ass!'He was supposed to be my special friend.
So 3 more returns to Nulb with a dominated Otis confirms he leaves the party no matter what. Guess it's time to either let him go, have him meet with an accident, or have Jaroo free him of his compulsion.
Iirc, as long as you don't go back to Nulb, he stays with you. (I could be misremembering). You need to get it all done in the first or second go. (you can recruit him up to 2x) . The second recruit requires a few special triggers/conditions and can't have joined a faction,etc.