Mom(diabetic)has dry gangrene on toe. angioplasty failed, doctors say vascular surgery imposible(foot veins too small), how can we restore bloodflow?

Maybe not: Typically, diabetic vascular disease involves the microscopic blood vessels of the foot, so even in the event more blood flow gets to the foot, it can't get through the obstructed outflow that occurs in these tiny blood vessels. This is one reason why bypass won't work in some diabetics. Smoking cessation is also very important, as is tight control of blood sugar. Hope this helps!

You don't: Gangrene is dead tissue. If there is gangrene of the toe, that part of the toe is gone. If there is poor blood flow to the leg, there are techniques to improve flow, starting proximally and going toward the foot. These may or may not work, but they are designed to limit the level of an amputation.