Ouch!
I'm really sorry to hear about your injury Pollychops.
Pleased to hear that you're still intending to get to Symi though and perhaps you'll find that you can enjoy a more sedentary holiday just as much as your planned walking one. Personally, I find that sitting in a bar watching the world go by is a very pleasant way to pass a few hours.
I'll be there at around the same time as you and if I see a chap on crutches clutching a Symi walking map and looking extremely frustrated I'll be sure to buy him a drink.