You are best adviced to avoid this transaction. It may lead to future chronic litigation

See since no chain documents are available i would not advice you to purchase the property as at time of resale or redevelopment there can be issues. 

1. It is not clear how your seller obtained title in the property.

2. However if your seller has interest in the property on the basis of sale agreement only then also he can sell the property and a good title can be passed to you if in the sale deed both seller and the developer join .

3. If there is no registered deed then mortgage of the property is possible. However to ensure your safety you may include indemnity clause.

It's total risk to buy such property, because it has unclear title.

Now you can take all mutation papers from revenue department from 1956 onwards till date.

Check who is true owner and under whose possession the property is.

If the possession person and Index II name is same than get first paper created from revenue department.

And search report and court report who is true owner than you can buy this property. 

Meanwhile you will come to know whether property is mortgage or free hold property etc.

You need to get the encumbrance certificate from the sub registrar offfice.  It's risky to buy such flats with incomplete title documents which can arise litigation in future. You can execute indemnity bond from the present owner in your favor

Dear client 

My suggestion is that you should not put your hard earned money to buy a flat from seller who doesn't have any papers of the flat. 

You can buy the flat if you can fight for ownership in case of some dispute arise in future. 

Seller does not have clear and marketable title to property 

2) seller had un registered sake deed which has been lost by him 

3) don’t purchase the flat as no bank is ready to give housing loan 

4) seller may have mortgaged original documents of title in his possession 

The seller does not even have a photocopy of the sale deed with builder?

His title is defective 

You can buy at your own risk 

However you will have an upper hand while negotiating the consideration 

You may get this flat at a discount, subject to risk as above

This is my response to you:

1. In simple words: NO, DO NOT PURCHASE;

2. If it is a genuine transaction, it will create a lot of problems for you;

3. An Indemnity bond will not serve long term purposes;

4. You can a do a title search of the property through a lawyer;

5. Consult a local lawyer, discuss full facts and take steps.

It is not advisable to buy a property from the seller who is not having a clear and marketable title to the property.

Unregistered title document is not reliable and even the registrar will not register the property now if you are going for registering the property.

The sale agreement even if found will not be of any use because it is also not a title document.

Hence  it is advisable that you better keep off from buying this property.

1. As per the information mentioned in the present query, makes it clear that the sale deed was there and when sale deed was there then it means that the flat must had been registered as sale deed is itself a proof of registration.
2. And yes, public notice and the copy of the FIR would serve your purpose.
3. And yes, you can get all the details pertaining to the flat from the office of the registrar’s by paying a nominal fees in some few rupees along with the application for inspection of records with respect to the specific property.
4. In fact, if you wish you can also try for getting the duplicate copy from the office of the registrar’s where the property is situated as there was sale deed so there must be some records for the same.