Why did the South African government end apartheid in the early 90s?

I know there were many strains such as international sanctions, a stagnant economy, and unrest in the townships, but couldn't the government foresee the mess of a country that was going to be inherited in five or ten years time? Was de Klerk the person who was mainly responsible for setting up apartheid negotiations? Do you think that if someone else more hardline than de Klerk were president that apartheid would still exist today?