My own recollection: yes, ZLMB was one hell of a good forum. It was moderated by a panel that included devout Mormons, never-Mormons, and ex-Mormons, which gave the moderation team a healthy mixture of perspectives. The mods tried very hard to lay down rules which ensured that everyone had a voice and issues were discussed rather than people. They made a sincere effort to avoid the flame wars and personal attacks that you see here, but it also did not capriciously ban people left and right like you see at Juliban's forum.
It had its flaws. I was an "undercover moderator" there, and in retrospect, I don't think undercover moderation is a good practice for any forum. The moderators should be known to the community so that their actions as individual moderators can be questioned and judged as needed.
I also think that the public "complaint forum" (or whatever it was called) was a very bad idea. Posts should be reported to the mods in private and the issues weighed and dealt with in private. There was no need for the circus of posters publicly dinging other posters.
3) If yes to #1, what could be done to bring something like it back to life?
Any forum such as ZLMB is going to have numbered days for two reasons:
(1) Mormonism is a comparatively small religious movement. Those who have things to say in criticism of it far, far outnumber those who have things to say that are positive or in defense of it. Any forum with "open enrollment" (so to speak) is going to eventually have an abnormally high critic-to-defender ratio, no matter how fair the moderation is. Few people enjoy participating on forums where theirs is the minority voice, where any post where they say something positive about their religion is answered by a dozen negative posts. Even if all of those negative posts are perfectly clinical and polite, it can still be overwhelming. The natural outcome for forums like these is that participation from believing Mormons declines. The conversations become one-sided and, without counterpoints, the critics get bored and leave, too.
(2) It's not just a numbers thing. Not only are Mormons smaller in numbers, but the critical voices often have the better arguments. Mormons tend to be stuck holding the bag on defending positions that are blatantly, obviously inferior or self-contradictory to just about everyone else. It doesn't matter how well a Mormon argues that position; it will always be the losing argument. And let's face it, no one likes to lose all or most of the time.
Those weren't the only reasons ZLMB failed, but they were certainly factors.
Someone could start another forum like ZLMB. If s/he got enough capable, substantive posters to agree to participate in the beginning, it might even have a few "glory years" like ZLMB did.
But I think, ultimately, any forum like ZLMB will go the way of ZLMB, for the reasons I outlined above.