So, the first time after ringing the bell, I got Szass Tam down to "badly wounded", at which point he said something like ok, you've been enough of a nuisance, now pick your stuff and leave before I really get angry. This dialogue implied that I should have been able to get away from the place. But Szass Tam remained hostile and, in fact, immediately after the dialogue, proceeded to destroy my party by using his "wish followed by a lot of nasty spells" strategy. So, this looked like a bug.
The second time, after reloading, I got him down to "near death", at which point he said something like right, get away RIGHT NOW (using lots of capital letters) and teleported me back to the clearing in Amn. I got no quest experience reward. No journal entry. Nobody (especially Neera) said anything about having solved this damn problem with the Red Wizards. When I check my journal, this whole business is still very much an unsolved quest, although of course there's no way I can get back. So, this also looked like a bug.
Anyone else seen stuff like this?