I've been in a few for various reasons. There's one where they choose a few redditors at random and you get 7 days to talk amongst yourselves, after that you are banned from the sub forever. That was amusing. Kinda gutting when you get the ban notification.
If you met someone who you really enjoyed talking to, what would stop you from staying connected to that person after the 7 days were over? You would know their username, right?
You absolutely could, but that feels weird after you've kinda just met. It's not like having a one to one chat with people, I think there was like 15 or 20 people?