If a Club Leader leaves, the leadership will be auto-assigned to a random Co-leader. If there are no Co-leaders in the Club, it will then be auto-assigned to a random active member.

There is currently not a way to pass Club leadership onto another player while remaining in the Club. However, if you plan on leaving your Club and there is a particular player who would like to take over the role, you can promote them as the only Co-Leader before leaving the Club. This will designate them as the leader after your departure.