1) if original lease cum sale deed document is missing has any police complaint being lodged?
2) was public notice issued of loss of originals
3) do you have certified copy from sub registrar office
4) on demise of owner has property been mutated in name of legal heirs
5) contact a local lawyer . he will drfat the sale deed for purchase of property .
6)you can approach bank for sanction of loan for purchase of property on the basis of documents in your possession . bank will do due diligence before sanction of loan