Deleting all assets related to Image Effects from your project whilst the components are on an object in your scene does not cause those components to update to "missing script" or similar. Game screen is then frozen (or black if you resize it) and component UIs broken until scene is saved, project is re-opened or similar.

Console receives one of the following errors per pass on each image effect shader:

"Invalid pass number (<PASSNUMBER>) for Graphics.Blit (Material "<SHADER NAME>" with 1 passes)"

Expected: Component UIs change to "missing script", all effects are removed from game view and it is refreshed.

2. How we can reproduce it using the example you attached

1) Open attached project and scene "ImageEffectAssetDeleteBug"
2) Delete everything from Assets directory
3) Notice how IE components on Camera are still visible (but UI is broken)
4) Try placing a cube in front of the camera. Camera preview will see it but game view will not (frozen)
5) View console for errors