Tenant Not vacating house in bangalore

Hi All, My Tenant informed me about vacating the house,and did not pay rent for 3 months to be deducted from deposit.We made a lawyer write a rental agreement and it has 100 rupee stamp on it signed by us and tenant which says in case the do not pay rent for 3 months they have to vacate .I have no idea if its a valid one as no registration was done. We found another tenant to occupy ,now current tenant says he cannot vacate as his job offer might come in a month to relocate to USA, will pay more rent money in case we need but he need not stay for 6 months or may be less so asking for 1 months notice again from us as his plans changed, the new tenant is relocationg from another state and they have agreed to our terms and conditions for a period of 11 months .As per agreement 11 months end by 24th March 2011 for the current tenant .What do we have to do as precautions in case they have not vacated by 31st of march .