I believe you (and the ex-Alliance) are going to be SOL, so would suggest you try to convince your former alliance mates come join you. Customer Service is not going to help the situation. We've gone through a similar situation in which the leader simply rage quit and has not logged in 5-6 months. After several requests being denied from CS, we simply moved and created a new alliance as we felt there was no real alternative given that the ex-leader was not responded to private messages either.
Was a real shame as the larger group has been together for close to 4-5 years over a number of games & chat apps.