Would this be a possibility?
-Make a Discord server, or use the existing Sc2mafia one.
-Have there be a Category that is invisible to everyone but a bot.
-Call the category "FM Chat Archives", and have the bot copy paste mafia and dead chat, when a FM game finishes, in a new text channel.
-Have the ability to ask for access to one of them for 24 hours by typing something like "!Access 356".
Alternatively
-Have a section in the Archives called "FM Chat Archives".
-A bot copies the chats over there once a FM game finishes.
I realize it's not very needed. I'd bet none of the 1000+ whatever communities that play FM archive their mafia and dead chats - and nobody ever had a problem with it.
But I think it'd make for a nice feature. Someone would have to make that bot though.