Required judgement if are-1 misplaced

Show cause notice is to be replied, 

you have to establish that such records have been misplaced, and show enough proof to rely upon, viz police FIR, news paper publishing of lost documents, and if required indemnity that whenever you get such records, you will handover to department.

side by side, shipping bill you can get from bank, where you have submitted the documents for payment. and you have 5th copy of ARE-1, which is endorsed by excise and customs both, which displays the authentication of documents.

you have to submit every possible document that goods cleared have been exported is genuine, and if needed the department can go for counter verify the same from customs station from where the goods have been exported.