This is why inactive mailboxes exist. If you think that even a smidgen of a chance exists that you will need a mailbox past the 30-day deletion retention period, you put it on hold before you delete the account. The mailbox will stay in place and available for recovery as long as the hold exists. That being said, to answer the question, no - after 30 days (approximately) the mailbox is removed and cannot be recovered, unless you use a service like Spanning.com to take online backups.
