Missing 2nd owner original sale deed in chain of registered sale deeds

I am buying a builder floor in Gurgaon. Seller has constructed 4 floors (Flats) on the land and selling them independently. Seller has got approval from HUDA for same. It has turned out that seller has got his property transferred and registered on her name from her husband and husband's friend. Prior to seller, her husband and husband's friend were registered owner of the property (Plot). It seems her husband and his friend have lost their original sale deed. Although they registered a complaint about it in local police station but never published any news paper advertisement nor submitted any complaint or affidavit in registrar. Also they never got any certified copied issued. Now bank is also rejecting the loan on purchase of a floor/flat built on this property. As bank wants atleast two original sale deeds in continuation. 1. Can there be ay chance of fraud in this purchase? 2. Is it possible that after losing the original papers, they just transferred and registered the property on wife name to just to sound more honest? 3. What kind of future issues might arise? 4. Can risk be eliminated by just getting a certified copy of lost original sale deed or still there might be legal issues? 5. Only 5% advance payment is done, so is it advised to cancel this purchase.