When you delete album you do not delegte the actual photo, only it's pointer in the album. It's like iTunes' playlists. You have only 1 actual photo file (in the Event) but can have many alias versions in albums, books, etc. See the Note at the bottom.
Deleting Photos from an iPhoto Library
1 - from an Event or the Photos mode: select the photo(s) and use the Delete key to move the photos to the trash bin. Then empty the iPhoto Trash bin as follows:
2 - from an album, smart album, book, slideshow, card, etc.: select the photo(s) and use the key combination of Command+Option+Delete to move the photos to the trash bin. Then empty the trash bin as above.
NOTE: deleting a photo from an album, slideshow, book, etc., with only the Delete key only deletes that photo from that item. Deleting a photo from an Event deletes ALL occurences of that photo in the library.
I second, third or whatever, the suggestion on getting an external HD (formatted OS X Extended (journaled) with ownership set to be ignored) and engaging a backup strategy ASAP.
OT