Is there not a way to view previous conversations in the chat? If not, then notes/a transcript will be the way to go.
Admins can check the chat logs whenever they like. They could just copy/paste the log into a thread. I also suggest that if these meetings will happen more commonly, maybe create an additional chat channel for it and only make it visible to members during a meeting.
What i meant was making a chat channel for these meetings, but only make that channel visible for actual meetings. This would make it easier to summarize each meeting into a thread, and keep the general discussion and meetings seperate.