it is up to the management to accept resignation on humanity grounds, because the medical evidence is submitted.
However the management has option to get harsh and ask the employee to buyout the two month notice, but it appears a willful harassment by management to other employees, balance if the employee has submitted an acceptable medical document, then management has to have a lenient view always, and release the employee, however if the management has some pending assignment / works with that employee he may ask the employee to finish the same asap , or make it transferred to some other employee with full details.
Getting always harsh is not in favor of employer, unless any incident happens towards breach of code of conduct.
A healthy working atmosphere can be generated with co-ordination between employee and employer only, otherwise it would generate chaos and will effect the ambiance of workplace