You can still close it but ebay will not finalise the closure until they are sure your account balance is ZERO, especially if you might owe them any money from recent sales. They will send you a message once it has been finally closed.
Until that time expires you will still be able to log in and view account status etc but you will not be able to buy or sell anything.
After it has been finalised the ID can no longer be used nor the email address associated with that closed ebay account in the future.
By that I mean it can still be used as a seprate email address to send/receive emails independently of ebay but can never be associated again with any other ebay account.
