Office 365 "Online Archiving - Enable or Disable"

Here is some more information - 

"If you disable a user's archive mailbox, you can reconnect it to the user's primary mailbox within 30 days of disabling it. In this case, the original contents of the archive mailbox are restored. After 30 days, the contents of the original archive mailbox are permanently deleted and can't be recovered. So if you re-enable the archive more than 30 days after disabling it, a new archive mailbox is created."

Further details are here - https://technet.microsoft.com/en-us/library/jj984357(v=exchg.150).aspx.  Hope that helps.