Reanimated bodies don't turn to dust when you use dead thrall for permanent zombies. You can keep recasting it on the body you want. svcks if you run into a necromancer and they get to it before you, though. Still, this is awesome news for those who like necromancy!
Doesn't think also mean that you can have a dead thrall permanently use an amazing weapon of yours? I have read that you can "give" a weapon to a dead body, and then when you use dead thrall on the body, it starts using that weapon. Of course, if the body turned to dust when it died, you wouldn't want to waste an expensive weapon on and lose the weapon when it died, but in this case, the weapon should stay with the thrall. So you can keep conjuring an indefinite summon with an optimal weapon.