I think this is a bug that's started popping up recently. It used to be if the leader died or aged out of club requirement, someone else still in the club would become the new leader, but I've noticed this has stopped happening, and I end up with leaderless clubs running around that I can't get into to edit or anything because like you said there's no leader to usurp. I haven't found it in the bugs page, but then I'm really bad at finding things there (search feature is NOT my friend). But I think it's just a bug. I'd report it there if it hasn't been already.
