extension of lease agreement

dear sir, we have a lease agreement with a housing society for a period of 99yrs.I would like to know 1.After 99yrs I will have to restore possession to society.In order to retain possession if I make an agreement with the Chairman of society now regarding the renewal terms after expiry of lease agreement will it hold good.for eg: a Agreement on Rs 100 stamp paper stating lease can be renewed subject to payment of Rs 50000 renewal.Hence is it a valid second agreement for extending period of lease, when already there is Lease deed to that effect for 99yrs.Will this second agreement entered now has a good legal standing for extension when period of lease is over.Pls advice if there are other terms.. 2 I have heard a lease above 30yrs is considered perpetual lease and hence I can get good title of land.After period of 99yrs my survivors can ask court to treat it as perpetual and hence extend my lease period or treat it as sale deed.Is this true. 3..kindly let me know how our family can retain possession of this land after 99yrs as we have paid considerable amount as non refundable amount for this land and we pay a yearly rent also towards it. Pls advice.. Vikas