Can you open Exchange System manager on the BES and can you manage the Org?
When you say you managed to send a mail from BES Manager to a test user where did you do this from and how? outlook cannot be installed on the BES so did you open its mailbox from somewhere else? in which case this just shows that its mailbox is alive.
Check the GC the BES is using - is it the DC that died? :
BlackBerry Search Results