Job Abandonment?

I had an employee call in with "car trouble" excuse last week and they have not shown up for work since. I also noticed that employee in question pulled down photo's of his family from their corkboard. I have not had any verbal communication from them. I did recieve an email stating that they are unwell and depressed and that per doctors orders, they will be taking some time off. I replied stating that they must produce a doctors note, since they have been absent for 3 consecutive days and have not heard anything since. The person in question has been with us for 5 years, they have exhausted all allowable sick and personal time. Any suggestions on how to handle this?