Every day I log into the game, the Spiral Uplink has a message about the Casino being opened. I haven't heard anyone on the forums or in guild chat talking about it at all, and there was no post on the Announcement forum.
According to the wiki, it returned a few times in the last couple months without any announcements, but this just seems weird. Why wouldn't they just take five minutes to write up a forum post about it?
Yes, it's back. I've found it few times in the Arcade on 12th, but I think I saw a Slime Key in Basil's shop a day before. I don't know if it means that it was here also on 11th.