When you use the Exchange Management Console to retrieve a list of disconnected mailboxes, you get an overview per server. Using the Exchange Management Shell it is fairly easy to retrieve a list of all disconnected mailboxes, regardless of the server on which the mailbox is homed. Using the Exchange Management Shell cmdlet Get-MailboxStatistics, you can get next to an overview of mailbox sizes, number of messgaes, and last time a mailbox was accessed, a view on the date mailbox was disconnected by filtering on the property DisconnectDate.
The following single line will give you a list of disconnected mailboxes, their mailbox database too wich they belong, and when they were disconnected.
Get-MailboxStatistics | where {$_.DisconnectDate -ne $Null} | ft displayname,database,disconnectdate