Dear Nishant Gandhi,
If the employee has gone on leave despite it not being approved, you can use remedy under Law for the same.
Now you have two options - a) If its possible, ask the employee to resign asap. Give him his dues and experience certificate and the case is closed.
b) If you want to follow the book ; You can also chargesheet the employee or insubordination, disciplinary issues. However, for this you will need to follow the procedure by the book. It will take approx. 02 months to complete the procedure and if found guilty, employee can be terminated or a suitable disciplinary action be taken. But if you wish to opt for this method, then you should ensure firstly that the reason for insubordination can be justified and is valid. To check this - please refer to Mr Divekar's post wherein he has given suitable questions to be asked to establish the claim.
Please let us know which option is suitable, if you wish to chargesheet, then I can give you the detailed process for the same.
Regards,
Deena Jagasia