I don't actually have any idea about how group chats are implemented in Tox, but I don't see why you can't send messages to the people in the group to redistrib

I don't actually have any idea about how group chats are implemented in Tox, but I don't see why you can't send messages to the people in the group to redistribute when people get back. It sounds like it might have history consistency issues, but maybe they already do that. I assumed you were talking about one-on-one message relaying, which is probably what most people would care about. That can't really be solved, since one of the goals of Tox is also to prevent 3rd parties from being able to tell who you are talking to. Can't do that if you have to broadcast to users "send this message to <x> when they get back"...