It had to go - it was buggy as shit. XF integration didn't work, and even though I'd turned off half the features (like the boing, being able to create channels and so on), people were still able to use those features. Sad though, it looked pretty neat and had some nice embed features that'd have allowed it to be used as a shoutbox with channels... Assuming those features actually worked.
It may come back depending on if their support can resolve it.
EDIT: And while I'm here, IRC plugins rely on IRC. Which is fine but it means everyone needs a separate login, and mods would have to login otherwise we lose the channel / their rights (which has happened before when the #codex channel was taken over once and nobody cared). Ideally I want something integrated with XF so there's no extra login required.
CometChat's known as the biggest resource hog among the chat addons. I tried several and most of them vary in bugginess only in the span between "very" and "moderately". For a site as large as the Codex though, any chat addon running completely locally would probably put a lot of load on the server, so I'd enable it just for logged-in users. I ended up installing ArrowChat on my site that's relatively decent, though also very buggy. When it works, it's nice though, stripped of all the nonsense nobody needs. Support's crap and bugs take forever and a day to get fixed, if ever, unfortunately.
The vBulletin integration was very good, though - the install was fully automatic and went without a hitch. Only took a few relatively simple manual fixes for avatar display in chatrooms.