I joined The Dark Brotherhood and I put my stuff in Astrid's room (cause I thought it was mine and it was a safe place to put it) but as you may know, the Sanctuary gets destroyed! I put the Ebony Claw in the wardrobe, and during the quest where you fight through the sanctuary the inventory of the wardrobe resets. How do I get the Ebony Claw back without resetting or cheating?
You can't get it back without reloading an earlier save, or spawning it manually, or using a mod.
PS3 and 360, load an earlier save, restart or ignore that questline.
If you're on PC then find the item code for the Ebony Claw and then research the console command for spawning items.
If you're on PS4 you could try the All Dragon Claws mod, which creates a safe at the trader in Riverwood with all the claws in it.
On XBox One you could try the Cheat Room mod which apparently contains all the in-game items.