perfect 
I finally found the thing @Stan_Pancakes
I made a small vid for showing the thing:
I confess this appears to be a misuse of blender.
I can believe blender devs didn’t prevent stupid users ( like me ) from doing stupid things. I think i did it by error but i did it. and this messed up my scene.
at the 0:11 time, you see in the vid the parenting of the cube to itself…
Reproducing the thing is quite easy
new scene
create cube
create sphere
select sphere then cube so that both are selected and cube is the active obj
parent with CTRL+P
select the cube
open relations tab
click on probe in parent fiel and select the cube
here you see ‘no parenting done’ ( wich is normal ) but the cube obj now have 2 users !!!
select the cube
hit ‘Suppr’ key
the cube disappears but the sphere parent seems ti still be here
and the cube data is still present in the blender file tab of the outliner.
This scene with deleted cube cannot be imported into unity3D.
However, blender still works like a charm as if nothing was wrong
Hope you like it 
Happy blending !
EDIT:
ahahaha 
sorry fro the green vid !!! it comes from the webm ( the forum don’t show MP4s ) coming itself from a gif capture app… 
reminds me the old days when we were working on autocad on green displays