I really like Corrupt as-is, personally, and I don't see a reason to make it NPC-Only if it maintains all of its Necromancy goodness. Pretty much any NPC Necromancer intended to be a major threat is going to pack at least one of them, and a however-wide Earth column of other nastiness; I feel like making it NPC-Only is just going to make any Corrupts that would normally be put into that column get turned into Deaths instead, which kind of runs counter to the "PC hit by it still gets to play" intention?
On a semi-related note, Corrupt pauses the death timer, so you technically have up to 10 minutes to take them down (the duration of the effect), plus 5 minutes after that to Life them. (Page 44 of the .10 packet, for reference.)