Haven't the African bishops already done that, in fact if not in name?
Taking a Catholic perspective, Robinson never was properly consecrated as a bishop because the Anglican Church lost its sacramental episcopate when it lapsed into the Protestant heresy.
He can't be unmade what he never was.
" Haven't the African bishops already done that, in fact if not in name?"
I don't think so. If they had, they would have broken communion with every bishop in communion with Robinson. As +Theodore the Studite recalled, +John Chrysostomos loudly declared not only heretics, but also those who have communion with them, to be enemies of God.