If North America would not have been in his way, Columbus and his men would have perished before reaching Asia.
Had North America not been in his way, Columbus and his men would have perished before reaching Asia.
If North America would not have been in his way, Columbus and his men would have perished before reaching Asia.
Had North America not been in his way, Columbus and his men would have perished before reaching Asia.
The structure "had North America not been in his way" is perfectly correct and is an appropriate way to introduce a contrary-to-fact hypothetical event. The structure "if North America would not have been in his way" is colloquial, and not up to GMAT standards.