Looking at vampiric Touch, a similar spell.

"You regain hit points equal to half the necrotic damage you dealt"...

And looking at the wording of this abilities I would rule or is similar to vampiric Touch and have the hp regeneration be based on the amount of damage dealt, nor in the role to deal damage.

Looking at vampiric Touch, a similar spell.

"You regain hit points equal to half the necrotic damage you dealt"...

And looking at the wording of this abilities I would rule this is similar to Vampiric Touch and have the hp regeneration be based on the amount of damage dealt, not o. The roll to see how much savage is dealt.

I think that ability could have more explicit wording as it can be interpreted two ways unlike vampiric torches wording.