Documentary evidence enough to win a case?

My father purchased agriculture land 25yrs back through registered sale deed but he didn't do mutation of the same. Seller son took advantage of this & got name changed in revenue records after his father demise. Seller son has also signed registered sale deed as a witness(not as consenting witness). Seller son is saying that they didn't sell the land but only gave documents as surety for a loan, which they also claim that it has been paid and forgot to take documents back or cancel registered sale deed. my deceased father migrated from the village 20yrs back and i know no one trust worthy in the village to call as witness. My question is 1) Is it compulsory to have a witness? What are my chances of winning this case without producing a witness and with only help of registered sale deed and other documentary evidence like EC from sub registrar office, land tax receipt?