I had a duck with the same type injury. It eventually didn't look as bad but never did the webbing grow back to what it looked like before. It thickened up and the foot resembled a regular chicken-type foot. It did not in any way impede his ability to swim. I never did know exactly what tore the webbing but I suspected turtle or possibly the other male duck as they used to fight quite a bit. As long as it doesn't get infected it should be okay.