Infiltrative BCCs are often wider and deeper than they appear to the naked eye. I would strongly recommend surgery and suggest Mohs surgery by an American College of Mohs Surgery member. Cure rates for Mohs approach 99%. PDT will likely not penetrate deep enough to treat your tumor and has a much higher recurrence rate.
The symptoms you are describing are not typical side effects from Botox and are most likely unrelated to the injections. I'm sorry you are not feeling well, if the symptoms continue I would see your primary care doctor.
If the scar is thickened or red, Biocorneum (or other silicon scar products) can still be helpful. It should be massaged into the scar twice a day for 6-12 weeks. If the scar is flat and white or depressed, it will likely not help. In that case a fractionated laser could be helpful with texture.
Given that he has been treated for an infection and it is has not improved I would consider a diagnosis of erosive Pustular Dermatosis (EPD). EPD is an inflammatory condition that can occur after significant trauma (such as from surgery) to the scalp. It is typically treated with very strong topical steroids and should improve. I would recommend follow up with a Mohs surgeon or board certified dermatologist.
If the scab is starting to lift at the edges, I would expect it to fall off within the next 1-2 weeks. Do not attempt to pick or pull it off as that might damage the graft underneath. I would keep the area hydrated with vaseline. I would recommend following back up with your surgeon though so that they can make sure you get optimal cosmetic results.
