First off, he needs a vascular workup and an angiogram, if the workup shows that there are adequate blood vessels, then a bypass may be in order, but a foot is not always able to be saved. The other thing is to get involved with a wound clinic that has hyperbaric oxygen, sometimes this treatment will aid in the salvage of a foot. I have not seen what the foot looks like and there are times when only amputation is the correct treatment, if the infection is too extensive. The problem with diabetes is that the small blood vessels are destroyed and the foot is numb and the damage/infection is usually sever before it is discovered the key to foot salvage is oxygen delivery to the foot and control of the infection.
I wish you luck with this, but start with a good wound clinic or a vascular surgeon.
As I say a lot here, you should ask the person doing the procedure. First, are you allergic? Second, is there a large volume of local to be used? If it is a simple mole removal, then probably not. The complications are a local infection, which I have never seen in many years of practice. There is pain at the time of injection and that goes away rapidly. Another question to ask the provider is what type of local is being used? They have different lengths of action, and of course where on the body it is being used. The best answer is to ask your provider and they should take the time to answer all of your questions completely.