Photos was unable to open the library “Photos Library.photoslibrary”. (-1)
Accidentally deleted photos app and already emptied the trash bin... what do I do?
Did you delete the Photos app, or did you delete the Photos Library that's normally found in the Pictures folder?
Was the extension .app, or was the extension .photoslibrary? I think (but I don't want to try it) that you can't delete Photos.app.
If you deleted the Photos Library, then that is gone. You can create a new Library by closing Photos, then you option-click the Photos icon, and choose Create New from the Library dialog.
Then you can import pictures to the Library.
Let us know if it was or wasn't the Library that you deleted...