Tbh, it seems less regen neg, and not even just destroying him beyond his ability to heal, but more like, even if he regens, the dark ki will just destroy him again?
"It'll destroy you at a cellular level no matter how many times you regenerate", and he specifically notes it as a dark ki property in reference to said attack (aka, it aint like he's claiming he'd just destroy him again and again with a dif attack) so it's def something *****.
The way it's worded confirms that the regen isn't being negated given the mention of no matter how many times he does it (as in, that mf can still regen), so at least ya right there, but it still seems to be hax kinda where it's a continuous attack or automatic trigger that stops it anyway, not regen neg but still a sort of hax.