[Taqwus]

None of those, I believe. Even a pure Life Drain attack will damage a lifeless unit, if memory serves, although it will not heal the attacker. Even if they were completely immune to a life drain, a Wraith Sword will still do ordinary physical damage as well.

Corpses can still decay, and even the Banefire Sceptre does just that as well IIRC -- heavy physical damage plus a decay effect.