petition is not approved after RFE asking end client letter

I had H1 b that expired in Sept 2012 , I had never travelled to US on that visa. My empoyer had applied for H1b under cab exempt and USCIS is asking for RFE end client letter . The client is not giving end client letter .

Now that I have received the RFE asking end client letter in case if petition is not approved what are the options that I have ?

Can I apply under cap exempt through another client or employer ?if yes when can I apply if no what shall I do ?

Yes, another employer can file cap-exempt petition for you either now or in future.