What's the best way to maintain a writable DB slave which is always overwritten by the master? I need to replicate our main server's databases (MariaDB) to a local server in our office, which will be used as an offline mirror when we have connectivity issues.

The data on the master should always take priority over the data on the local slave. Our users will be instructed never to write anything to the local "offline" slave, however it will still need to be writeable to enable auth &amp; sessions.

I believe that with a standard Master-Slave setup, this will create problems with data consistency.

Short of writing a shell script to drop &amp; re-migrate all of the databases, &amp; reset the replication logs when the connection is re-established, is there a better way to configure such replication natively with MariaDB or Galera?
You could use symmetricds to perform the bidirectional replication. It allows for conflict management in which you can define which side wins in the conflict in your case the master.