Validity of Sale deed executed by the agent/ holder of general power of attorney.

My father gave a General Power Of Attorney (GPA) for land plot to his friend on March 2nd 2005. Among other powers my father explicitly stated that GPA agent can sell the property if he finds a profitable deal. He gave GPA because my father is a member of the chit scheme run by the friend who is holder of the GPA. GPA agent demanded a security or support for the advance my father received from the GPA holder. The GPA holder entered into a sale agreement with his blood related uncle on behalf of my father on 8th of July 2005. On 8th of April 2008, my father cancelled the GPA. On 5th of May 2008 the GPA agent executed a sale deed based on the sale agreement entered on 8th July 2005 to his uncle. My father came to know about this sale later on. And since GPA agent was a known friend, my father tried out of court settlement to resolve the issue, as this was the practice in most cases in our locality knowing the legal route will take years to get justice. It happened for quite long time as my father to approached the registrar to cancel the sale deed, but they refused to do so. Finally my father filed a case in 2017. Till now the case is going on. My father died on September 1 2020 due to COVID. We have petitioned to run the case on behalf of my father by providing legal heir documents. These are some brief facts and timeline of events regarding our case. Our layer says the chance sucess in our favour is 60%. He is of the opinion that my father should have filed the case within a specific time limit( mentioned in some law) from the date of knowing the incident. I need a second opinion from layers who are expertised in property law and GPA cases. I also googled and found that the supreme court of India in 2011 and 2019 held that property sale through GPA are invalid. In light of the above Judgement, I want know how strong our case is and whether the judgement will be in our favour.