According to new ESIC; employees whose salary is less than 21,000 slab will cover under ESI, that is statuary rule as a mandatory; if an employee leave the company automatically the ESI contribution is also stopped, so the employees will no longer enjoy tge benefits of ESI.
ESI is only useful and helpful if the employee works under a employer who opted ESI according to labor and established act.
hope this can helps you, in simple terms, if employee wants to use ESI, they have enroll to ESI and still continue to work under a employer.