User blog comment:1dra7/This is a plan to save the wiki, k?/@comment-1510769-20121230131954/@comment-1874924-20121230185315

I'm going by the chat roster that I see on the Activity Feed, among other pages. As far as I know, that roster does not distinguish between group and private chats, because people on a private chat still have access to the main chat.

In Frank's case, I'm guessing that either his interests have changed or life got in the way, or both. It's somewhat common for people to leave for months at a time for either or both of these reasons.