When you refund your Fortnite Crew subscription the content you received will be removed from your account. This includes the cosmetic items from the Crew pack, the 1000 V-Bucks, and an additional 950 VBucks to cover the cost of the Battle Pass (the Battle Pass will remain on your account, along with any earned tiers).
If you do not have 1950 V-Bucks in your balance, other cosmetic items in your locker may be removed to cover the balance.
If you still wish to keep the cosmetic items that were removed you can add the required V-Bucks to your account and contact Player Support to have the V-Bucks deducted and items added back to your locker. This does not apply to the cosmetic items from the Crew Pack.
Note: If you cancel your subscription nothing will be removed and it is all yours to keep! Items will only be removed when you receive a refund.