[Baalz]

Yeah, the thing is there is no such thing as a un-killable SC, that's the way the game is designed. Your unkillable SC could obviously fail a MR for a soul slay, or disintegrate, or be hit by another SC, or simply be banished to inferno. VotD is designed to be a SC stopper, but even still is only that effective (referring to a time limit death) if you have:
An astral + death mage
A guy who has killed hundreds of people
Who also has a low enough MR to be vulnerable (just try to cast it at an in-dominion god with a lead shield, starshine cap, and amulet of antimagic)
Who also doesn't have aoe damage that hurts undead.
Who isn't expecting it (because you've been casting it for a couple turns), and scripted something more appropriate to dealing with hoards of undead. (returning, wrathful skies, etc.)

Plus, it always targets the biggest kill count in a province, so if you start getting hit by it you only need to set up one "shield" guy, and you know who it should be.

Sure, Mind Hunt is counterable...if you have astral mages. In some situations though mind hunt can be completely devastating. Many spells are devastating if used in the right situation.