Dead Thrall raised a NPC level 40 max (level 50 if you have Vampirism/Necromage) and he will fight for you. The timer on this VERY long (Thousands of hours I think), so pretty much till he "dies". Anyway, when he does or the spell last, you can recast the spell on him, as he doesn't turn to dust.
Careful, the Dead Thrall doesn't act like a follower, you cannot command him like you command your follower. He is a high class summoned undead with skills. he can be a mule for you, but to load/unload him you need to kill him first and "loot" the corpse. He cannot use the armor you give him, only the armor he is wearing before he dies the first time. He can SOMETIMES use weapon/staff you give him.
Also, you though that followers are bad at sneaking? Think again. Dead Thralls, even if you choose one with high Sneak skill, are like elephant playing trumpet in a glass shop.