It is still completely possible for Google to use hashed passwords to authenticate users and only "save" the plain password in a "write only" file (text or separate database) with the unhashed passwords...
Yes, but this is stupid and really gets rid of the point of having the hashed password in the first place. Now you have two copies, and even better if you hack the french data you start potentially having information necessary to recover passwords from other more secure countries. As for the 'write only' file, seriously? the only write only file is
Well in fact you CAN create write only file. Simply make private/public key pair and store public key in the server (the one that you can only encrypt data). Keep the private key on safe location away from the server. So now server can write to DB with public key but it's imposible to decrypt it and when officials want data they can pull private key from usb stick for example and decrypt it.
You will have many recoverable tape errors.