If you forget your encryption passphrase - Your encrypted data will be unusable. Forever. 

This is the way zero-knowledge encryption works - The only person who can access the files is the person who knows the encryption passphrase.

This is why we highly recommend using something memorable as your encryption passphrase - Making something long, complex and hard to remember, easy to forget is not the important part here - Your passphrase gets converted client-side into a secure 256-bit encryption key for your data.