Following the end of Apartheid and the enfranchisement of black voters, could De Klerk's nationalist party still have won against Mandela's ANC in the 1994 South African elections?
I don't think they could have. It wasn't just the blacks voting for Mandela, it was a bunch of liberal anti-apartheid whites who also voted for Mandela being the 'new South Africa', as opposed to De Klerk's ties to the old apartheid regime. Even if the numbers were even, De Klerk's bunch just had way too much baggage for people to vote for them comfortably.