1) Issue legal notice to seller to execute registered sale deed in your favour 

2) if he fails to do so file suit for specific performance to direct seller to execute registered sale deed in your favour 

3) in the alternative to refund Rs 50 lakhs paid by you with interest 

You have to file suit for specific performance to direct seller to execute registered sale deed 

1. If you are not interested in this agreement then you can send cancellation notice and seek refund.

2. Otherwise you can file suit for specific performance of contract.

Yu can choose either of the two options. 

you will have to file a suit against the seller for refund of your advance with interest 

essentially you will have to seek a declaration that the sale agreement stands terminated on non-fulfillment of obligations on the part of the seller

even if the sale agreement is not registered you can still sue the seller for refund of your advance as that would be a collateral purpose for which you want to rely on the sale agreement that you had paid an advance. Thus vide the proviso to s.49 of the registration act, non-registration of the sale agreement will not come in the way of the proposed suit to be filed by you

as regards your follow up, if the time limit for registration of final sale deed has expired then the parties by their conduct can always extend the timeline. In this case you have to decide whether or not you want to enforce the agreement against the seller by requiring him to register the property in your name or whether you wish to rescind from the contract on account non-fulfillment of obligations by the seller and seek refund of your advance with interest. So it is a choice which you have to make

1.  The seller has tried to cheat you and also the earlier buyer whose sale agreement is registered for the property in question.

2.  If the seller and the earlier sale agreement holder don't cancel their sale agreement by registering cancellation Deed, then subsequent non-registered sale agreement executed by the seller in your favour will not have any legal validity.

3.   Send a legal notice to the seller for cancellation of the earlier sale agreement by executing registered Cancellation Deed in the jurisdictional Sub Registrar's Office or to reimburse the advance amount of Rs.50 L + interest for the duration of the advance amount with him + penalty clause if mentioned in the sale agreement.

4.   If the problem still not resolved, complain against the seller for cheating in the jurisdictional Police Station.

5.   Unregistered sale agreement is not legally valid.

6.   The legal validity of the registered sale agreement is three years.

You can file a suit for specific performance and get the directions from court 

Dear client, a sale agreement is valid without registration for three years from the date of execution. You can claim the advance payment and damages from the seller as he made sale agreement with another party. If the 6 months of time in the sale agreement has expired then the agreement will become void as the limitation is mentioned in the agreement.

Sale agreement will expire after 6 months. Send him legal notice to register sale deed or refund of amount with interest. 

Since he has made a sale agreement with other party as well so he has committed cheating with you. Also intimate him of police complaint. 

It is not advisable to proceed with the purchase of this proper without cancelling the previous registered sale agreement.

You have to insist and compel the seller to get the previous registered sale agreement by executing a registered cancellation deed jointly along with the previous buyer.

The unregistered sale agreement cannot be enforced in law though it can be used for the purpose of evidence for the sale agreement or receipt of money hence you may become eligible for getting return of the  advance  amount.

You have two options:

1. Issue a legal notice to the seller one week prior to the last date of the sale agreement demanding the seller to executed the registered sale deed in your favor while expressing your ready and willingness to perform your part of the contract by paying the balance of sale consideration amount and to get the sale deed registered at your cost;

If the seller is not responding or not complying with demands made, you may file a suit for specific performance of contract seeking execution of sale deed with an alternate prayer for refund of advance amount with interest.

2. The second option is to wait for him to respond till the expiry of the sale agreement period, communicate the decision to cancel the sale agreement and then demand him to return the advance amount with interest till the date of settlement.

Failing to comply with this demand you may file a summary suit for recovery of money and seek for attachment before judgment of the property as security towards the advance amount.  

The limitation for the sale agreement irrespective of the time limit mentioned in the sale agreement is three years.

Hence you can proceed choosing either of the option suggested above in my previous post .

It is advisable to obtain a proper legal opinion before venturing into any option.

- Yes, the said unregistered sale agreement is valid for the recovery of the paid amount from the seller 

- Further, even after the expiration of the agreement period this agreement will be valid limited to 3 maximum period for filing the case 

- If he not complied the terms of the agreement then you can send him a demand notice /notice for for specific performance. 

-  Further if the seller has already sold the property to third party , then you can even lodge an FIR against him for the offence of cheating and breach of trust.