If you set a very strong password on a Bitcoin core wallet consisting of both lower and upper case letters, numbers, and special characters there's no way of recovering the password unless you can remember some parts of it.
On the other hand, if you set a weak password of just lower case letters, and can remember some details like its approximate length, or some characters it contains, then someone runs a password recovery service that might be able to help.
These are links to its bitcointalk thread and website. He charges a fee for password recovery, but seems trustworthy. He's been running the service for years now.
https://bitcointalk.org/index.php?topic=239665.0http://walletrecoveryservices.com/
