That’s sucks and I’m so sorry either anything above or get in touch with the leaders family and have them help but that seems impossible and disrespectful
My sincere condolences to all who loved your leader.
As a game mechanics issue, there is no means in-game to replace an inactive leader. Support may be able to help, but the simplest way is to create a new alliance and port everyone there underva new leader.
Oh no, that is so sad 
. My condolences to his family, friends and your alliance 