About Herc

If Herc was split in half, I think the two halves would just fuse back together. As for his entire body being destroyed, if it was just split into pieces, he'd probability get up casually, but if his body was completely destroyed, I'm not completely sure he'd come back. Its not really determined(from my knowledge, feel free to correct me if I'm wrong) if herc' ability was to regenerate from fatal wounds or literally revive from the dead. The first option, herc is dead. He has nothing to regen from. If it's the second option, he's probably coming back, as it would just be another death and new body would probably be coming back soon.

It's depend on Hercules Master
For example here in FGO any servant you play will become broken, because Ritsuka/Gudako ( we as the pilot ). While on other Fate series, most master can't Exploit his/her servant power so well.

Warning, a bit of spoiler here !
Hercules in FGO is on another level with her/his past master.

With Ritsuka/Gudako ability, Herc can even solo Goetia with an NP power of 1000 Excalibur.
Goetia destroy him, obliterate his body but Herc back to fight again to protect Ritsuka/Gudako.

Another example here few master have witness Gilgamesh Enuma Elish.
But in our hand Gil can freaking use those EX level NP as we wish to and Gil give her/him the permission to do that.
Or worse we using Artoria Saber to defeat entire KOTR Camelot army including Lancer Arthuria. Yes Gudako/Ritsuka a bit cruel.

No matter how strong your servant is, it's up to his/her master.

A very powerful attack is supposed to be able to wipe out multiple lives on Herc, which was what happened in the Fate route when Shirou and Saber used Caliburn against him. I would imagine that if an attack was powerful enough to turn him into dust or split him in half, it would likely wipe out all remaining lives and he would just be dead.

One thing about the F/SN you are misinterpreting is thet is not about number like the marvel universe.
Its fair in marvel to calculate the actual value of thing, but not in f/sn,
All Power in F/SN are Conceptual. This mean their effect is going to work reguardless logic, unless another conceptual weapon or power interfair.
Hercules resurrection is a proof of his strenght, and even if he is complitly destroyed he will came back.
Actually, in the fate route we have proof of this. Saber activated excalibur inside of herc body, and i dont have to explain what thet mean. in fact he died for thet attack 7 time, becouse he keep on resurrecting himself before the attack was over (and becouse it was one attack he dident had time to become immune .... poor herc)
Sorry for my eng, hope i was able to prove my point on this topic.

in fact, Shiro/Saber destroying 7 lives of Herc in a blow was Plot Ex Machina, since otherwise they had no chance to win, and you cant kill protagonist mid-game.

and technically, he do not even need to regenerate.. Throne of Heroes can just clone the Soul and re-duplicate him

In the UBW anime it is mentioned that God Hand is not directly healing but rather works by reversing time.
The wiki has a comparsion to vampires that mentions
"This ability operates under normal conditions and causes the vampire's body to regress through time to its original vampiric state whenever it receives an injury"

After a quick read on the Fate route's battle I failed to find any mention of the mechanic so I'm not entirely certain if it is verified.
I'm also not able to confirm the vampire part but I remember it being enough to regenerate an entire body from a pair of feet.

Based on that assumption of the NP's mechanics it should indicate two things.
The first is if an attack managed to completely destroy his body but failed to remove all lives then Herc would rewind once again.

It would also prevent him from cloning in creative ways.

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I wonder if it would be possible to bypass the NP's effect by using something like Ciel's Seventh Holy Scripture.
I'm aware that the difference in age and concepts would prevent it from harming Herc but would God Hand extend to spiritual damage or is it restricted to merely physical?