Why should an employer doubt that the employees intention to resign. If the person said "Enough us enough, I'm not up to the job any longer" why should they query his decision? The Department is obviously better off without someone who has been ill for a length of time, and his mental illness may affect the particular job he is employed to do, particularly in the public sector. Without knowing what the terms of the employment contract are I can't see what it has to do with it either. So now he/she has changed their mind and wanting the job back. This is business, no room for emotions, times are hard, someone who has probably taken a lot of time off work is not going to be looked upon favourably. Even if they knew the extent of the illness, why should they take him/her back now? Obviously the person needs treatment before being considered for employment again. Sorry if this sounds hard but this is purely an opinion not any kind of legal argument.