It is possible to delete imported address with private key from encrypted wallet without entering the password. I dont know how this is possible - it shouldnt be that way. The private part of wallet should be encrypted so it should not be possible to mess with it without password.
To be clear, this is just like deleting an encrypted file on your hard-drive. You can still see the filename and know where the file is while it's encrypted, and you don't need to decrypt it to simply delete it or overwrite it with new data.
Arguably though, certain operations like that maybe should soft-require a password to prevent legitimate users from doing it accidentally. But it's really only a soft-barrier: there's nothing stopping you, an attacker, or malware from opening the wallet file and deleting that entry.