Men and Women of the Imperium are neither slaves and neither slaves of a corpse, The God-Emperor is with us no matter where we go! PS: that is heretic, not Necron talk what you do there, know your faction!
Chaos or not, we know he isn't divine and that his physical body is mostly dead only his mind is still functional.
For what you need a functional body when your mind can inspire trillions of your people and can reach to every corner in the galaxy to lighten it up for your people? The Emperor has fought well in the Horus Heresy and he earned his rest, yet he still fights everyday for us his own personal fight to enlighten us further!
i have found one of your tomb-worlds, and am tea-bagging your sleeping brethren as we speak Necron > : D
LOL Also, we are/were slaves to no one. Even when the C'tan still existed, we weren't their slaves. More like less powerful allies (of convenience).