Hm, yes there should be some possibility of transferring command if the leader becomes dormant for too much time.
Coup sounds good, if the leader does not login for two weeks and a coup is initiated, the leader may be sent an email, then if he doesn't login in the next 7 days the leadership may be transferred to the highest power active player in the group.
mmm our leader is now approaching 1500h offline and still the group suffers...