When a Clan Leader hasn't logged into Clash of Clans for 90 days, the game selects a new Leader automatically.
Members, as well as the Leader, are notified throughout the rotation process via messages in the game.
60 days of inactivity:
74 days of inactivity:
83 days of inactivity:
90 days of inactivity
Only Co-leaders and Elders can be appointed as new Leaders.
Leader status will never be given to a Member, regardless of how long they have been in the Clan, their activity, or what ranks they might have held in the Clan in the past.
Below are the reasons why the Leader hasn't changed yet:
Support cannot rotate leadership on request.
If rotation can't happen in your Clan, your best option is to find or create a new Clan.
You only lose Leader status if you don't play the game for 90 days.
Even if you are inactive for a long time, you will receive screen notifications encouraging you to log in and manage your Clan again. This happens well before a new Leader is appointed.
To receive the screen notifications, you must have Clash of Clans currently installed, and notifications for Clash of Clans enabled.