Nephilim: What in the World Happened to the Biblical Giants?

Nephilim were giants in the earth according to biblical accounts. What ever happened to these Biblical giants?

Genesis 6:4 KJV

4 There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.