Chat rooms that have been inactive for a period of time and which have fewer than 15 messages are automatically deleted. This is a very reasonable thing to do in general, but not when the room was created to host a conversation that had begun in the comments.
When two users exchange too many comments under a post, they are prompted to take it to chat. However, this prompt can appear before they've reached the threshold of 15 messages that ensures that the room isn't deleted, resulting in rooms that have potentially useful discussions relevant to a post being deleted for inactivity.
Since we already have users complaining that the only reason we want to move stuff to chat is to shut them up, having their discussion deleted after they did The Right Thing® and moved it to chat doesn't feel right.
So, I am proposing that if a room was created by moving a conversation to chat, it should be protected from autodeletion no matter how many messages they contain or how old the room is.