Arbitration mailboxes in a hybrid deployment

Hi,

We've migrated all user mailboxes to Office 365.  I would like to retain our on-premise Exchange 2013 server to manage active directory objects (as recommended).  However, I would like to delete the mailbox database in order to free disk space, and if possible remove the mailbox server role.  What should I do with the arbitration and Discover Search mailboxes?  Can they be migrated to Office 365?  I haven't been able to find instructions on how to do that.  I could move them to a new database on-premise, but would prefer to keep our local environment as lean as possible.

Thanks!

Dave