The master policy is usually with company.
Keep the death certificate, proof of being on company tour, proof of deduction of premia from salary/CTC, doctors certificate showing cause of death as Heart Attack, postmartem report etc safely.
Your uncle might have nominated some family member in policy and might have kept the copy in record at home.
Nominee may Submit, under proper acknowledgment), the declaration of death to MD,Head-HR of the company and attach death certificate and ask to supply requisite forms to claim, if any, and claim money.
Nomnee is only trustee and is obliged to share proceeds with all ClassI legal heirs.