I wanted to take the time to summarize and answer your questions of "Why is chat gone?"
Chat has been temporarily disabled on Brickipedia for one week due to the numerous negative interactions between users in chat. There have been many conflicts and arguments in chat and on the wiki from occurrences in chat. This disruption to the wiki itself is why the admins have disabled wiki chat.
This is merely a short summary. This decision was made by wiki administrators on the admin wiki. Please ask further questions, if any, in the comments.