I (and maybe you, but I cannot see your opinion sufficiently) would not vote for any ANC president.  And this is ONLY an ANC decision; presumably they would appoint Ramaphosa as caretaker president while they all jockey for leader in Dec 2019.  And if Ramaphosa does a halfway decent job in the next two years, perhaps the ANC will survive in the 2019 elections.  And if he cannot bring the ANC back from the Zuma years and it becomes clear that the new ANC post Zuma is no better than the Zuma ANC, then the electorate will punish the ANC.