Originally Posted by qtzar
The two BES's will be at different locations so what happens if the internal WAN link to the SQL server goes down and the BES server can not communicate with the SQL server?
The BES will complain and throw errors in the logs about not being able to communicate with the database. The BES will continue to function, and mail will still flow, but it's not exactly healthy to let it run in that "disconnected" state for very long. If the disconnect is longer than a handful of minutes... you might want to consider taking the BES down until your WAN links come back up.
Before you do this.. It's best you make sure your WAN link is somewhat reliable, with low latency.