Hello @nurudeen adeboye ,
When an Exchange Online license is removed from a user, Exchange Online data associated with that account is held for 30 days. After the 30-day grace period, the data is deleted and can't be recovered. If you add the license back to the user during the grace period, this will restore access, and the mailbox will become fully active.
Source: https://learn.microsoft.com/en-us/exchange/recipients-in-exchange-online/delete-or-restore-mailboxes
Assuming not renewing your subscription also means that the users are no longer licensed with a valid Exchange licenses. They will have their mailboxes permanently deleted after 30 days.
There is no way to recover data from such mailboxes past the 30 day limit. Even support won't be able to help you in such scenarios, but you can always open a case, just to make sure you've exhausted all options.
Check this answer as well: https://learn.microsoft.com/en-us/answers/questions/623579/office365-recover-mailbox-data-for-unlicensed-user.html
Regards,