H1B RFE - Within how days it need to responded?

I filed for H1B this year and I got an H1B RFE and withing how many days we need to respond to the RFE.

Another question is if it get rejected or not respond to the query will I get my money back

Typically it is 12 weeks as per USCIS recent update. Read the USCIS RFE processing time update

Nope, USCIS does not. It is employer's expense.

Will I be able to withdraw the application and in that case will my money refunded?
I am hoping that that I will not be able to get the client letter which is mandatory I believe.In that case is it advisable to withdraw the application?

My lawyer is asking for the experience letter from my current company and previous company in their letter head which it will be difficult to get it.Is there any other alternative to overcome this.