Moot. D negs regen. Period. There is no exception.
On the contrary, you haven't shown anything. You made the claim D can kill Alucard so he couldn't regenerate, but you fail to explain how D could prevent Alucard from regening by:
a) his millions of souls pre ending
Again, moot. D cuts space/time. He busted out of a sealed dimensional space which created anomalies across time/space all throughout history. It created the Bermuda Triangle and made ships disappear. Jack the Ripper vanished in a time distortion. People in the past saw t he future, people in the future saw the past, and various other temporal distortions.
b) his quantum "being anywhere" as long as he remembers himself power. (And how you think this means he can simply teleport places is beyond me.)
But this in itself is a no limits fallacy.
. You can't use a no-limits fallacy either. Once in Left Hand, you don't exist anymore.