Okay, I was wrong. The scenario is currently possible when you take multiple mages into account, one a dark mage raising animals as zombies, and the other a beastmaster casting Joined Strength on said zombies. This would only occur in a team game though, since you wouldn't have reason to cast Joined Strength on an opponent's creature. So I suppose we do need an answer to the rare scenario. Again, my guess is that you just wouldn't count the damage dealt to the non-living creature and only heal for the part dealt to the living one. So, attacking the zombie animal with a vampiric attack would heal you 1, due to the 1 damage transferred to the living mage.