I had a subtalar fusion last year and I too tried to put it off but it was the best decision I've made to date with this ankle. Those take your breath away pains are gone!
I did put it off a bit and the Arizona brace was absolutely a life saver for that but the brace wasn't intended to solve the problem, just helped me not be in pain or make things worse before surgery.
If you are in that much pain, odds are you don't have much motion in that joint now so you won't miss the motion. This joint isn't like your tibiotalar talar where it's going to effect your hips, knees, etc. so don't let that be a deciding factor in your decision. Also compared to other surgeries I've had, pain from surgery/recovery wasn't too bad either - always a plus.
Cortisone shots are great for short term pain relief but unfortunately they wear off and you are back where you started. Not sure the rationale for putting off fixing it, unfortunately it most likely is not going to heal. Time to get your life back!