I need some help understanding archving in Office 365 and how deleting mailboxes (to recover licenses) affects the archived data.  We are using AD Sync to manage accounts.  What is the best practice or your recommendation for disabling/deleting mailboxes for terminated users in Active Directory which synchronizes to Office 365 and still retaining the archived data.  I have limited # of licenses for which our budget will allow and I want to avoid having to purchase licenses for users and mailboxes not in use.  

I hope this makes sense and that someone can help with some guidance.  Thanks!