I would not expect McCain to get anywhere near 50% of the black vote...there was a similar rift between Cleo Fields and Mary Landrieu in Louisiana, but in the end, blacks sucked it up and voted for Landrieu.
What I mentioned is what I have been hearing from blacks that I have talked to personally or in other forums. I am from Louisiana also and remember both Landrieu and Fields. I remember when Fields ran for governor against Foster and lost. I don’t know how many black Obama supporters you have personally talked to, but about 1/2 of the ones I talked to said they have no intention on voting for HRC (this also includes the blacks in my family). They either would vote for McCain, another candidate, or just sit out.