After the flood, did all the Nephilim die? What about the mention of "giants" in the story of Joshua and the spies? What about Goliath?
The Bible says that all those outside the ark of Noah perished in the flood:
Gen. 7:20 The water prevailed fifteen cubits higher, and the mountains were covered.
Gen. 7:21 All flesh that moved on the earth perished, birds and cattle and beasts and every swarming thing that swarms upon the earth, and all mankind;
Gen. 7:22 of all that was on the dry land, all in whose nostrils was the breath of the spirit of life, died.
Since no Nephilim were on the ark, therefore all of the Nephilim died in the flood. Furthermore, the Bible confirms that only the righteous by faith survived the flood (again on the ark), and all the ungodly on earth – including the disobedient angels and their progeny (i.e., the Nephilim) – were cast into Hell:
2Pet. 2:4 For if God did not spare angels when they sinned, but cast them into hell and committed them to pits of darkness, reserved for judgment;
2Pet. 2:5 and did not spare the ancient world, but preserved Noah, a preacher of righteousness, with seven others, when He brought a flood upon the world of the ungodly;
Therefore, all Nephilim were condemned to the Abyss and await their final judgment there. None survived the flood.
To learn how the spies reported Nephilim, please read our article.