If the database is mirrored, the way you have it set up should be fine. However, if the database is only mirrored one way, historical data can be a problem: when it’s written to A, it will be mirrored. But if A goes down and B writes to database B, the data will not make its way back to A.
A potential solution for this is to set up a second database connection for history only that points to A from both machines. When A goes, B will continue to run status/SQLTag stuff, but will cache historical data. When database A comes back up, the cached data will be written.
Hope this helps,