Shared Albums are completely separate from the Library. Deleting pictures from albums doesn't delete them from the Library. What you're describing is extremely odd. There's no "Select All" in the Library (and I now understand why,) so it would be hard to delete every picture.
Have you looked to see what's at iCloud.com? I would also double check to be sure that you are connected to the same Apple Account that you were before-- like in a magic show, looking the other way may make things seem to disappear. Who else has access to this account?
I would also check the Filters in the Library view as well as the sorting to be sure you haven't filtered everything out.

Deleted pictures remain in the "Recently Deleted" view for 30 days, and then they are removed permanently. This safety feature can be defeated by choosing to prematurely delete pictures from the "Recently Deleted" view. If you use iCloud Photos, then that "synchronizes" its Photos Library with the phone, so what you see on the phone is what is at iCloud. iCloud Photos doesn't keep pictures in "Recently Deleted" any longer than the phone does.
You can see this:
If you're missing photos or videos in the Photos app - Apple Support
Basically the above says to look in Recently Deleted and in Hidden.
If you don't keep your own backups to an external drive, then there really isn't any place else to look.