I havnt been working with UE4 for about three weeks now and I just noticed that my skysphere is gone… I havnt deleted any files.
At the bottom right of the content browser click view options, check the box that says show engine content, you can then search for BP_Sky_Sphere within there, and I believe it will come back in the quick place panel by itself at that point…
often happens when deleting actors in top or side view, since you cant see that you have it selected. Quite common.
by searching ‘sky’ in modes, you are filtering in the wrong place - search in the scene outliner to verify it is in fact gone. If it is, re-add it.