Can I purchase the Battle Pass after canceling the Fortnite Crew?

Yes, you can purchase the Battle Pass after your Fortnite Crew billing period ends.

The LEGO Pass and Music Pass can also be purchased separately.

To cancel your subscription, refer to How can I cancel my Fortnite Crew subscription?
For information on how canceling affects access to premium rewards, refer to Why did I lose access to the new Battle Pass after canceling my Fortnite Crew subscription?