Not Serving Notice Period

One of our Employee resigned from his position the same day he received his salary and next day he came office to handover office stuff and after spending hours convincing him to serve notice but he didn't listen and left without serving notice period. We have 90 days of notice period as per employment terms but we waived off 60 days and asked him to serve 30 days notice but he denied it. Later on, we mailed him to either serve notice period or pay 30 days salary. In reply, he gave his medical certificate stating that due to my health issue I am advised to stay at home so kindly release my salary. In reply, we mention that considering your health you can take rest for 6-7 days and resume workstation and serve notice period or pay 30 days notice amount. Before he left he already accepted an offer from another company and he is giving excuses for his health. We are Solar industry and in the developing stage so just now we crossed 10 employees and so we just received S&E registration. The only reason to take action against this employee is that he is 5th employee who resigned without serving the notice period. Just to stop this attitude of current employee we want to take such harsh steps. Those 4 who left have genuine family issues because all were from outstate but he is from same state and wants to stop this practice of employees. In this scenario as an employer could we send a Legal Notice to him and are there any chances to win the case? Kindly guide on the same.