Baurus showed up at the arcane university when I got the third book (I had exited first edition books and fast traveled to the university). He says follow me I know the way but then won't leave the university area, even when I open the gates for him.
Poor guy seems lost, but any ideas how to make him go? I tried many things, including going down to the sewers myself and sitting at the table, but the cultists never show up.

Well, I was about to give up on main quest.... no saves before that encounter...
I slept on it (in game, not life ) and he appeared in elven gardens! It's a miracle!
Not before I spent a night fighting him - which isn't a crime, and getting all the mage apprentices killed in the process (I never was charged since his accidental swings lead to numerous brawls with all the mages while I watched them kill each other and picked up their stuff

He follows you after you start the quest and talking twice activates it.

Nah, man he didn't do that at all, no matter how many times I talked to him, or if I opened the gates and walked out, or if I did...... anything. As I mentioned, I went so far as to clear out the sewers and sat in the chair for 30 minutes real time. It wasn't going to happen at that point.

Essentially, the programming rescued the game for me by resetting his position to the Elven gardens while I slept so I could go to him. I think I nearly broke it because the game is designed to have him pop up right after you get book #3, but I so quickly fast-traveled to the Arcane U that the game didn't know how to get Baurus to get from there to the Gardens. He just kept walking that crescent up around the arch-mages tower... but no worries. Next time I'll just stay in the bookstore (1st Edition) a little longer and wait for him to show up.

He once followed me all the way to the town at the very southeast. I was being attacked but he kept telling me to go. Lucky for me, he died in the quest.