Sale deed issue

When the deed is registered means he appeared before registering authority , there will be identification in the registration order and besides the witnesses to the sale deed they will testify. The money transaction and receipts

Simply he is allegating or serious if it is in your possession don't be afraid if he goes to court defend it by leading evidence through hand writing experts in court .

The vendor cannot claim or raise any such issue at this belated stage.

It is barred by limitation.

Besides, even if there is any possibility of impersonation, what made him to remain silent for all these 15 to 16 years without taking any action.

Has he filed any suit for cancellation of sale deed ?

Under whose possession is the property now?

You may revert with more details for more opinions.