It will not stand legally 

Dear,

         It will not stand legal.

         Ask insurance company to give you in writing about this incident.

Can ask for fresh declaration but cannot repudiate for own wrong. Complain to IRDAI grievance cell.

No, in case your Insurance claim is repudiated you have to go to the consumer forum and complaint regarding this this is the responsibility up insurance company to keep the documents intact and the client cannot suffer because of the mistakes of the insurance company please claim the insurance claim amount along with the compensation and legal charges

If the insurance company has clinching evidence to prove that the life assured was suffering from some major ailment/disease prior to taking the policy of Reviving the lapsed policy, non-disclosure of the aid particulars in this connection can be treated as suppression of material facts for taking policy or reviving the lapsed policy.

Therefore the insurance company is right in repudiating the death claim 

No insurance company cannot repudiate your policy. Because it doesn't stand legally.

It discripency om their end not from your end you can complaint to ombudsman of IRDAI.

1. As per the information mentioned in the present query, makes it clear that the insurance company has misplaced the documents.
2. But, as you talked about repudiation then I would like to guide you that it is your discretion if the company is unable to keep the documents safely then there is no point in continuing.
3. Yes, you have the option and your step wound also be legally correct.