Gift Registration Issue

Sir.. My sister got married in 2001. My father purchased a plot and registered on her name as marriage gift. My brother in law harassed my sister and registered the plot on his name without knowing by my father. Due to his continuous harassements we brought our sister to our home. Some elders from both sides demanded him to register back the plot on my sister name. So he registered back that plot on my sister name as gift registration.My sister sold that plot to others for financial need (she has a daughter) After several sequences, sister got diversed with him, after divorse that guy filed a petition that he want his gift back. We filed counter & he didnt followed the case properly, so case is disposed. Now he reopened the case, sending court notices to our home, but my sister married other person and staying peacefully. We rejected the notices 2 times by reason of she is not staying with us. What happens now if we rejecting notices and if we not follow up this case...?? What are the consequences...?? Please guide me...