Well if the potential hero of whatever where to be aborted or whatever, there could probably be another hero like the Hero of Winds (Wind Waker Link) Or the Spirit of the Hero (Skyward Sword Link) who has to go through numerous trials in order to save the land.

Oh and dont ask then what if there was no one because all the men were cowards or untrained or all the female Hylians decided to abort and kill their sons because they want a female hero to save the land of Hyrule for the sake of sexual equality instead of piece...