First, I want to say that it would not be professional behavior to leave your job in this manner. You are currently on leave, which implies you are supposed to return to work on February 1, 2013, after the completion of your granted leave period. However, planning to quit now because you have received another job offer is not acceptable. If you have found another job, you are supposed to resign first, serve a notice period, and then go on leave.
It would be considered unprofessional and unethical if you were to leave without serving the notice period.
You can approach your employer on February 1, 2013, after completing your leave period, and explain to your boss or HR personnel that you are unable to return for valid reasons. Request to be relieved from your duties, but ultimately, this decision depends on your employer or boss. By persuading them, you may be able to take the next steps in joining another company. Otherwise, they may not provide you with a relieving or experience letter or necessary exit clearance, which are essential for joining a new employer and may be verified during a background check.
Understanding your current situation and considering the future implications is crucial.