1. See the agreement could not be complete because of the condition of lockdown it's an executable agreement and buyer can take ground of force majure as things were not in his hand. Therefore, you may after lockdown if lifted give a notice or inform the buyer giving him some time to complete the condition in agreement and can register the property in his favor.
2. See there is no defined period but the agreement could not be completed due to kickdown therefore you may grant him reasonable time and notify same to the buyer if on notice if he fails to respond then cancel the agreement as per procedure of law.