Ghosted by Employee

BC Employer here. We had an employee go on EI Medical leave in February (we dont have STD). When it came time to transition the employee to our LTD plan, the insurance provider declined the claim. Their deadline to appeal the decision was the end of September. The employee has stopped returning calls or responding to emails. The insurance provider is calling into question if the employee is meeting the definition of an employee if they are not on an LTD claim. How long can an employee ghost their employer before their employment is terminated?