After your alliance leader is offline for over 2 days, the next time a rank 3 member comes online, they will be automatically promoted to leader.

If the alliance leader is offline over 3 days and no rank 3 member has come online, the next rank 2 member to come online will be automatically promoted to leader.

If the alliance leader is offline over 4 days and no rank 2/3 members are online, any member that comes online will be promoted to leader.