Procedure to own rented property in case landlord unavailable.

Dear sir, I am a tenant living in a row house of a housing complex for more than 12 years. Nothing is documented like rent agreement etc. Earlier property was belonging to an old lady who died and then her long distance relative claimed it and made registration of house in his name(not sure) who was also an aged person. We met about 10 years before but since then he is not traceable to me. Neither he visited nor sent any communication for the last 10 years. I wanted to buy the house legally if he comes but we do not know his residential address or any other mean to contact him for further talk. I may also possible the demise of the person, so please help me out how to proceed in this case without opting for another property.