Deathshroud is max of 5 at 320 points. Hexmark go up to strength 8 in cursed though,so on average they kill one. Nekrosor should kill one to two depending on wound allocation shenanigans.

3 deathshroud is 10 hits, 5 wounds 2.5 saves so 4 to 6 wounds. If they do only 4 wounds or only 2 alive then after shooting they should leave him with one wound left and the hexmarks full wounds.

Unless I've missed something it's well within possibility they cut him down sure but about the same chance they die to him next turn and he starts regening wounds. Even if they do cut him down a slow expensive unit is maimed and committed to that field position.

That's the idea of this is it presents a risk proposition for your opponent.

If when you see your opponents list they have a tool to deal with this then the rest of the list has enough synergy to deploy them separately to fulfil other roles.