That would depend on whether the accounts were set up as POP or as IMAP, i.e. whether your mail is being stored locally or on the server. Obviously anything on the server will be gone when the accounts are cancelled… But you may avoid this problem entirely, regardless of the type of account, by creating custom folders under <b>Local Folders</b>, at the bottom of the list of accounts in the folder pane, to store and organise your mail locally on your computer there however you wish, independently of any account you may have. Mail stored there won't be affected by the accounts being cancelled or even by you removing the accounts from Thunderbird yourself.