Hi Ivan.
please don't freak out, I personally got audited and it went very smooth.
I highly recommend that you read the PMI FAQs about the audit it will clear all your confusions and will let you much more relaxed about the process. you can find the FAQs
Here
Regarding your concern, you should fill in all forms and send to client for signing. the client will send you the signed forms back which you will send to the PMI.
I just would like to let you know that you can have any colleague from the project do the approval if he is more reachable that the client, there is no obligation that the client must approve.
Good Luck