The difficulty I have with this concept is that the Flood was specifically designed to eradicate the situation where mankind was contaminated via angelic tampering.
That is right, and it did it's job.
But, Azazel and his 200 who rebelled were simply one class of rebelling angel. There are powers, principalities, and archons that also rebelled against God. I think I mentioned it here, but archons and principalities tried to make life in their own image, but failed.
So, they used human vessels to bring their images to life - kind of how the "facegrabbers" need a human host to incubate and birth an actual xenomorph. They did not have the breath of life to produce life directly, so they used human's inherent ability to bear children, and the power potential of a "child of God." If you recall the "Annunaki" story, it is very similar to what the principalities and archons tried to do. It is also referenced and alluded to in the Alien movie - especially prometheus and covenant. That, life was seeded, and the Annunaki made us from clay pots to mine world for gold.
In order for me to accept the scenario of Nephilim once more running rampant after the Flood would be to imagine God permitting of contaminated humans surviving which makes no sense.
Well, lets start with the fact that it is written that there were definitively giants after the flood - so it happened, and its purpose was to destdoy the abominations. I don't even remember the apocryphal saying the physical vessels of the hybrids survived. The confusion may come from lack of information and attention on the enemies in different dimensions. When the Nephilim, Rephaim, Enim and/or Anakim die, they become restless spirits that wander the earth seeking a vessel to inhabit. Dead nephiyl are demons; the spirit of those abominations are directly from their angelic fathers. So, they were physically gone.
But, we are at war; other angels, powers, principalities and archons rebelled, and tried to make life in their own image. It became nearly impossible to do it through regular Intercourse because God DID put in restrictions.
Him allowing this is a testament to our disobedience. We should know better, but even after the world ended we continued in abominable sin like nothing ever happened.
If we keep welcoming these principalities, archons and powers into our lives, why wouldnt they? Recall in the spirit your intent is enouth to condemn you; the hosts may have saw what the watchers did, but they figured they could do a better job. (Ironically, the Wisdom of God in the apocrypha scoffed at their attempt to make life in their image.) The fact that these entities can actually assault us is because
we give them permission to do so, or provide a loophole for them through sin. God and His holy ones are gentlemen; demons are not. Demons will invade. And, we have allowed them to do this to us because we qualify sin to make us feel better, failing to recognize any sin opens us up to oppression and possession even.
The lot that did Genesis 6: Part II participated in genetic manipulation and transhumanism, taking halfling remnant genetics and manipulating them (besides the humans that naturally introduced the manipulation through Intercourse and procreation.) "Ritual Magic," instead of direct intercourse, became the way to bring about their plans.
Or else not having set limits to that type of angelic interference after the flood and therefore making the Flood event totally unnecessary and useless.
You know God; He will let you completely embarrass and deplete your sinful self to completion, while using it to better those He loves. The watchers are in chains to this day. And, so is any other angel that has tried to procreate with man.
Right now the name of the game isn't direct procreation through Intercourse, it is genetic manipulations. The stories of grey aliens read exactly like demons extracting human DNA to create genetic abominations. Aliens being aliens is part of the great deception. They are interdimensional EBEs.
Furthermore, the angels who disobeyed in that manner are described as being restricted after the Flood.
They are in chains. But, more angels and powers tried it - as well as possible remnants left in one of the wives of Noah. Azazel and the 200 did Genesis 6. Powers and principalities can operate remotely and control their own demons, or angelic spirits. There is a hierarchy.
So I would also have to ignore that scripture in order to imagine resurgence of the identical pre-flood situation.
I would say you should look deeper in it. The canon clearly states that there were nephiyl in those days and also afterward. But, the canon is silent on the how.
That should compel one to dig deeper. In the apocryphal library, it is explained in tremendous detail what happened, why it happened, how it happened, and how they survived/were around afterward. The church has removed these books throughout the years arguing that they are heretical. It is a shame, because everyone is responsible for his or her own soul - not an earthly, religious hierarchy.
Also, it was not the exact same situation. Antediluvian hosts that fell relied on intercourse. Postdiluvian hosts relied on genetic manipulation, and blood magics (which, would be called applied medicine today.)
True, Jesus did say that the least days would be similar to the days of Noah. But he specifically specified what he meant by referring to the uncaring unaware attitude which preflood mankind had before the disaster descended on them.
That is how it started in the days of Enoch, Lamech and eventually Noah. There was no switch flipped, and all of a sudden everyone was uncaring. The nephiyl were violent, and ate men. The hybrids made witches and sorcerers of the people by giving them sacred knowledge in exchange for a portion of their soul - sealed by a sexual or blood sacrifice. And, this activity gradually permeated all of humanity unt humans were more abomination than human, genetically.
And, these angels did not just genetically manipulate humans: they did it to birds, felines, canines, and other animals.
This is a spotted issue in general because it is something the canon is mute on, the apocryphal thoroughly details it (but is ignored/shunned by most all Christians,) and the topic is usually rejected violently should one want to speak about it.
So, most of us will not, and cannot win, because we do not know who our enemy is, what they are capable of, and how they behave - we barely agree that our enemy exists in the first place.
There are plenty omissions and alleged contradictions in the canon. But, even the mistakes are divinely precise in their ability to compel the reader to seek out the truth. Errors, mistranslations, and even purposeful omissions set up a perfect situation for the believer to not only dig deeper to find the truth, but to also recognize the assault on truth itself.
Another important thing to remember is
God has not killed/destroyed anything yet. No angel, no souls.