Definitely not a PT here, but what I would do is work on a lot of small motor strength in that leg - balance, ankle weights, etc. You might find tai chi-like poses and slow movement helpful. Looking at my anatomy program, it looks like that muscle area might do a lot with balance-y sorts of things and foot flexion, much more so than calf raises.

I'll also note that about 5 years ago I had a bit of the outer quad on my left leg (prolly the vastus lateralis) carved out in a car accident. I still have a noticeable hollow there, but the remainder of the muscle is fine, and it as well as the others in the area have taken up the slack. I don't know if the muscle groups below the knee will behave similarly, but they might. Which is to say that in the long run, having a divot taken out of a muscle might not impact your strength or range of motion.