One of the simplest ways to keep a user's mail after their Office 365 account is no longer being used is to convert the user to a shared mailbox. There are limits as to how many such mailboxes you can create, but this will provide a window in which the data can be transferred to another user's mailbox folders, downloaded as a PST, or backed up in some other fashion. Smaller companies may never hit the limit at all, or may simply decide after a while that preserving the mail is no longer important.
One positive aspect of this approach is that you can take advantage of shared mailboxes even in smaller companies that aren't leveraging enterprise plans in Office 365. Thus, if you have all Business and Business Premium ...
