Its a big problem for some Alliances. demote inactive leader after a long time,not bad idea.(need talking about how time).
there is some solution:
1-Inactive leader Demote after xtime(example 3month).
2-Not demote leader,but first coleader has power same leader after a long time leader inactive.
3-better way is :there is a option in alliance setting that leader can setup who can be leader if he inactive for 3 month.
but a way,ther must be a wat to solve this problem .