It depends on what the current contract says but, yes, it’s generally advisable to either terminate or amend the current employment contract, if there is one. The question of whether the employee would remain subject to ESA depends on a bunch of different things, including the employee’s job–might be exempt if it’s management or in an industry exempt from ESA regulations, whether they’re an employee or independent contractor and whether the terms of a collective agreement apply, not to mention the definition of “employee” under the ESA laws of your jurisdiction.