Although Clan Leaders may appoint Co-Leaders, these members have a smaller scope of abilities and responsibilities than Leaders.
Prior to the Clan's Leader leaving the game or taking a break, it's best if they appoint another member as the Leader of your Clan. Please note, however, that there's only one Leader function in the Clan, so the current one will lose the position if another member becomes appointed to lead your Clan to victory and glory. If the current Leader of your Clan becomes suddenly inactive, however, currently there isn't a way to replace them.
Such an option may be added to the game in the future. For the time being, an alternative solution would be to create a new Clan with an active player as its leader. More on creating Clans can be found in the article available here.
Regrettably, we cannot transfer the Prestige Points from your previous Clan to the new one. Please keep this in mind when creating this new community. It will be a fresh start, but the abilities of the Clan members, their knowledge, tactics and all the friendships formed until this moment are simply immovable and everlasting.