I am sorry to hear about this. It was a really good idea to password protect your data. Additionally, the My Passport model uses a hardware encryption. Without the password, whoever stole the drive will not be able to view your files.
However, the drive may be completely usable if the drive is completely wiped and formatted. When it comes to encryption and security, the My Passport is a very reliable drive and I advise you not to worry about your information. If a wrong password has been used more than three times, then the drive will lock itself and the only option will be to factory reset the drive, erasing all data.
If you have any more questions, feel free to ask me, or contact the WD Support:
Hope this helps