You'll have to go back to an earlier save. Generally speaking, any objects placed on top of another object (like a floor panel) that you scrap gets removed from the game based on my experience.
It 'counts' as +1 Luck,
you just can't put it on your stand.
if you are on PC, use the following console code to spawn another one.
Player.placeatme 00178B5A 1
So you did look in your workshop inventory and it's not in the MISC section? Generally when I scrap a crate or something with items in it those items get transferred to the workshop inventory. Items on top, I always assumed did the same, but haven't tested it out.
tried decorating a few times with objects.
they always seem to disappear.
found out they are not, actually.
Will bet you anything that bobblehead is somewhere.
look harder.
Ive had things "meld" into other objects; morph on the floor & get kicked around; appear in the ceiling; etc etc etc.
It's around, & possibly even 500ft away.
Just a matter of locating it.