I am The Compendium
From what I've read (and learned more about in school) was that angels on earth had sex with humans and the hybrids that were born were called Nephilim (or grigori or giants).
God then sent the flood to kill them. But when Moses and his followers were wandering the desert, they came upon a city (I think Midrash) and found giants living there.
Were these the same giants? What happened to them (according to The Bible)? Does the Bible say or insinuate that anything about what would happen if any Nephilim survived? Why were they so bad in the first place?
There are big enough holes in the Flood narrative to sail an ark through, the Exodus has no archaeology supporting it, and the Bible contradicts itself hundreds of times.
To answer your questions, though:
I am The Compendium
Were these the same giants?
- Their nature is complicated by the ambiguity of Genesis 6:4, in which it's unclear whether the "sons of God" themselves are the Nephilim, or their offspring are. The apocryphal Book of Enoch is the only thing that suggests the latter. It also is the most likely source for the commonly-held belief that they are fallen angels; the Bible itself refers to them only as "Sons of God".
I am The Compendium
What happened to them (according to The Bible)?
- The Bible doesn't really elaborate on what happened to them, but the Flood, since it allegedly killed everything that wasn't on the ark, should have wiped them out. The Book of Enoch actually suggests that eliminating them was one of God's reasons for flooding the Earth.
That said: Noah's Flood is in Genesis, which predates the book of Numbers 13:33 by a pretty long time, suggesting that...
A> Some Nephilim survived the Flood
B> The giants from Numbers are mistakenly called 'Nephilim'
C> More "Sons of God" had children with human women after the Flood
After this encounter, there's no further mention of them. Some suggest that the "Fallen Mighty" of Ezekiel 32:27 speaks of them, but it does not; the word used there is "nophlim".
I am The Compendium
Does the Bible say or insinuate that anything about what would happen if any Nephilim survived?
- Nope.
I am The Compendium
Why were they so bad in the first place?
- Nothing in the Bible specifically says they were. Their association with Fallen Angels comes from outside sources, such as apocryphal texts.
As far as God wanting to wipe them from the earth, "OT God" was an insular-thinking xenophobe who didn't want anyone worshiping anything other than him, so the idea of the offspring of some of his subordinates being legends among men prolly pissed him off.