You can't unlink the bank account from PayPal without adding another one. However, if you just closed the bank account, there's no way they'd know, once you've funds in your wallet and set thus as preferred payment method.
However, PayPal piggy back on the AML that the bank has already done, and use the bank account to verify your identity once your PayPal transactions reach certain levels. I'd also be thinking about how I'd ever get the money out of PayPal in future if the linked account was closed.
Are you closing the bank account because of fees?