There are about 20 different vessel configurations associated with congenital one artery anamoly. I don't believe there is any answer to what the blood distribution would be if the graft failed without more information. It may also depend if the failure is gradual such as accumulating plaque for an occlusion, or a blood clot that quickly interrupts the normal blood flow. Treatment could be a stent, or a bypass.
Hope this provides a perspective. Take care