Dear Mohit,
Have you gone through Revised CLAT 2018 Calendar it says that after the closure of the CLAT Office, vacancy if any, in any NLU will be filled by the respective NLUs at their own level from the CLAT list in the order of merit as per the Rules and Regulations of the participating Universities . First of all it's not necessary that there will be a vacant seat in every or any NLU . If that happens, in that scenario there will be no closing rank for vacant seats which can be expected for any NLU. In fact no body can guess that. I hope it helps!