A couple of thoughts on the subject.
1. The nerve he injured is the common peroneal nerve which itself splits into a deep peroneal nerve and a superficial peroneal nerve around the level of the knee.
2. While he has a foot drop there is more to the nerve injury than just that. That is only looking at the ankle as a hinge joint moving up and done. The ankle also inverts (twists foot so sole faces the midline) and everts (twists foot so sole faces outwards). The movement in eversion will be severely affected by the superficial peroneal part of the injury and can't be compensated for well in a brace or with taping.
3. There is some confusion about the degree of the nerve injury or whether the nerve was injured at all. There are 3 types and 5 degrees of nerve injury, roughly. The 3 types are neurapraxia (1st degree) which involves thinning of the outer insulation of the nerve, axonotmesis (2nd to 4th degree) which involves disruption of the inner wiring or axons of the nerves but leaves the outer nerve sheath physically intact and neurotmesis (5th degree) in which the nerve is transected.
Now Smith clearly has the 2nd type of injury, axonotmesis. This basically means the axons distal to the point of injury degenerated completely. However, we don't know how much of the inner architecture (endoneurium, perineurium and epineurium) were affected. If the inner architecture of the nerve is fully intact (2nd degree) he may get close to a complete recovery and on a reasonable timeframe. If there is 3rd degree injury there will be some loss of inner architecture, there will be scar tissue and the ability of the nerves to re-grown and find their way back to the muscles will be impaired to some degree and his recovery will be partial and probably take longer than the 1 inch per month figure which is usually a best case scenario anyways. If there is 4th degree injury that means much of the inner architecture has been disrupted, there will be a lot of scarring and nerve re-growth will be markedly restricted. Such patients will often have a later revision surgery to try and aid in recovery.
I think Smith likely has some 2nd and 3rd degree injury based on descriptions of surgical findings. How much is 2nd vs. 3rd degree isn't something you can figure out with current medical tests. If the Cowboys doctor thought it was probably more 2nd degree than 3rd degree than his thoughts on the subject could have influenced the Jones' decision as no one would know better than him as he visualized the nerve and how much deformation there was.
4. In terms of nerve regrowth, the important part is the gap between where the nerve degenerated to the motor point of the muscle. For the tibialis anterior that is fairly high up in the calf and the re-innervation there will end the foot drop. To get down to the peroneii which help with eversion of the ankle the nerve re-growth has to go down a bit further more like halfway down the calf. So while it is true that the main effects of the injury are on the control of the ankle, the nerve regrowth doesn't have to get all the way to the ankle for Smith to recover.
