From your query it is very clear that the sale agreement was never acted upon and that you have made an effort to repay the amount received as advance from the buyer . You must preserve these records and this will be a good defence, if the buyer approaches the court. Even if the buyer approaches the court for specific performance, he is unlikely to succeed as he has not bought the property within the duration of 2 months as entered in the agreement and you have made the necessary efforts to return the money due to him.
On the link you have mentioned in the earlier post, it clearly speaks of an " Indemnity bond " , which protects the interests of the buyer in the event the seller does not act upon the agreement. Hence this post is not applicable to you as the facts are different.
It is true that the Govt of Tamilnadu has made all sale agreements compulsarily registrable from december 2012 and this will inturn aid you, if you have made the sale agreement post december 2012.