1. As the tenure of the current rental agreement is coming to an end in three months, you can issue a legal notice to the tenant to vacate the premises right on the next day after the expiration of the rental agreement. You can mention the reasons that due to his bad attitude on many occasions you are not willing to renew the rental agreement anymore and inform him strictly to vacate immediately on expiration of current rental agreement.
2. We cannot predict what the tenant will do if she's filing a case against you but you can always demand the monthly rental amount in your reply to her case.
3. The unregistered rental agreement is not enforceable in law besides the renewal is the discretion of the landlord.