This is meant to be a somewhat-easier-to-digest recap of the discussion that can be found on the MikroTik forum at this URL: https://forum.mikrotik.com/viewtopic.php?f=23&t=157048&p=836497&hilit=failover#p836497 Note that the forum discussion not only addresses failover, but also load balancing at the same time (without explicitly saying so in the beginning).
For the sake of this document, we'll make some assumptions: