I would recommend to look at the fare rules of your actual ticket. There are many different fares with different rules for rebookings, cancellations etc. Then you know exactly what you are entitled to and how much it would cost you.
But illness is no special reason for a refund normally - unless the ticket rules allow refunds (sometimes for a fee) or date... changes.
If your friend booked one of these inexpensive non-refundable fares he most likely will be out of luck for getting a refund.

And if you need help finding the ticket rules post the fare basis here. They look like SL387LGT or QL376LGT and are found in the ticket information. I am sure somebody will help and post the rules here.