Best practice is to Make and keep regular and numerous back ups. If you have only one back up copy of your file, you have far too few back ups. Keep an up to date clone of the file with no passwords enabled. This won't protect data, but does keep your design accessible and secure.
Admin passwords really should be written down, presented to the owner or general manager of your database with instructions to put one copy in the office safe and one copy to be stored in a safe deposit box. Not only can this be forgotten, but the one guy with admin privileges could be fired, get a different job or drop dead of a sudden fatal health issue.
That said, I've heard of a third party produced product that is supposed to be able to insert an admin account into a locked up file, but with proper management of your system, you should never need it.