Did you ask if they would credit your funds to my booking and just re open up your spot?? Surely they'll get the spot booked anyway seeing as there is only 20 openings!! I'd be pretty disappointed in the mob if they wouldn't allow that especially given your genuine circumstances.
The email I got back,
G'day Ryan,
I'm sorry to hear about your injury and that you won't be able to attend our DirtWise School in July.
Unfortunately, we are unable to extend your deposit to another participant already registered in the class. If you are able to find someone to take your spot, we can use your deposit for them and you can work out the reimbursement of the deposit with them. They would just have to fill out the registration form and if you would let us know they will be taking your spot.
If you have any other questions please let me know!