If you are unable to use your Season ticket due to long term sickness you can return your ticket for refund at the point your sickness begins. Refunds can also be back dated to cover the period the absence began, if you can provide suitable evidence of the period you were unable to travel.
When you return to work you can purchase a new ticket for travel.
To apply for a refund go the My account section of the website and choose get a refund. Print the refund form and send it via recorded delivery along with your ticket to -
GA Season Tickets
PO Box 23971