Hi syam,
If u want to block the leads basing on the date in the lead serach result u need to enhance the lead search view.
In the event EH_ONSEARCH you will set the collection to the context node.
Before setting the collection u do a loop on the collection get the end date of the lead, check with the current date if it exceeds remove it from the collection, so now u can filter the collection basing on your condition now use the set_collection.
Thanks and Regards,
DP.