You should take backups of the data storage that Business Notification uses regularly (or work these into your existing backup schedule). The things that will need to be backed up are:
The SQL Server databases. Their names are:
BusinessNotification
BusinessNotificationInstanceMBSBN
BusinessNotificationInstanceNSMain
On the machine where the Business Notification Server is running,
the following file should be backed up: appADF.xml
If you installed the Business Notification Server to the default
location then this file is located in the following folder:
\ProgramFiles\MicrosoftBusinessSolutions\Navision\BusinessNotification\BusinessNotificationServices\AppDefinition