Payment by buyer to be made after registration of property

Hi, My father has a flat in Delhi and has "General Power of Attorney" of the same flat. We agreed to sell it off to a buyer. Buyer has paid the black money part of the deal , however, banks are not ready to finance it in absence of proper registration documents. Buyer's lawyer has suggested us to register property on buyer's name and the buyer will apply for loan and then balance amount will be paid by buyer. Registration documents will also have cheque number, amount, date, bank details etc through which buyer will pay us balance amount, but it will not have anything which says that "this registration documents stands cancelled in case of payment default by buyer". My question is, in case buyer does not pay us the balance amount , will this property registration stands cancelled?? and if yes, how can it be done. We do not intent to register the property first on my father's name as it will incur additional charges. We were told by few people that in case of payment default by buyer, registration documents stands cancelled. And additionally, can we make any affidavit between seller and buyer stating above situation?? Pls share a possible solution to this problem. Warm Regards Gurucharan Singh