On this, when Ryouta merged with Loki here it's stated that He (and probably Loki on his own) had the the abilities of all the witches, I just read the manga entirely and didn't see that, could you please post a scan showing this in case I missed it?
Even usual souls in Notch can revive after completely erasing from current plane of existence. So it's High-Godly regen.
Which sounds like it's talking about the old definition of high-godly regen and not the new definition.
If you know about the new Regeneration definitions then that's cool and I won't push you further, but if you don't, High-Godly has been changed from "Destruction of soul/body/mind and the realm where they reside" to "Erasure of soul/body/mind and all associated information". Your explanation just of that they can revive after having their soul and plane of existence erased isn't sufficient to meet the new definition.