I think this is a better way. My SN fam member is inactive, still has one planet, and I’ve sent a few friendly messages, but my last one was to please let me know if he’s playing so I don’t mark him inactive.
Simple solution there @audiodef. Watch the family council. If everything has remained static for days with the player in question, except for any NW increases from population and science research, then that player is inactive. Send an in game message asking for a reply within 24 or 48 hours. If do not get one, then mark inactive, attack and remove from the game.