Dear Mr. Shankar,
As per my understanding, it is mandatory to have the ESI coverage for your employees who are drawing gross salary below 21K per month when your organization is having 10 or more employees. Any other medical benefits may not be a replacement for ESIC coverage as most of the ESIC inspectors may not agree to your claim that your medical coverage offers better benefits than ESIC [in case, there is a medical insurance coverage policy which covers all the benefits that ESI offers]. As ESI is offering many benefits to the employees who are covered under it, I personally don't believe that it can be replaced by any other insurance policies. [sorry, if I am wrong.]
The medical insurance coverage policy will replace ESI in areas which are declared as ESI - Non implemented areas. This attachment may be helpful for you.
Thanks and Best Regards,
Syam