I was working on a big mod and without realising it, saved after having "deleted" a kit piece. i think it was CaveHall1WaySmRamped2. It's marked with an asterisk and a capital "D". Does this mean the piece is gone forever? and if so, is there a way to replace it? I tried dragging it into the render window, and it says the piece has been deleted. i went to Vault 22, and where the cave ramp used to be is an empty space, which falling into teleports me back to the elevator door.

ADDENDUM: It was CaveHallRamped2. thats what i may have deleted.

First obvious question, do you have a previous version of the mod to load?

As for replacing this, if you just deleted the reference to it for a cell, and not the asset itself, you should just be able to put it back. If you deleted the Asset, then you will have to figure out how to get that back. Probably by loading the original content you are editing. Hopefully you don't have to unpack a BSA to recover this.