Unfortunately there is nothing that can be done. If the Founder of the Group did not set up any Admins for the Group, only he can manage the Group/Clan. The Group/Clan and his bungie.net is his responsibility.
Unfortunately the only way to be added is for the Founder to add you considering there's no admins. Bungie cannot add you to the group nor give you founder. I'm sorry but it looks like it's a lost cause if the current founder is banned.