I think, however, that a disappearing back network
has no real consequences as the heartbeats always go over both.
FWIW this has not been my experience, at least through Luminous.
What I’ve seen is that when the cluster/replication net is configured but unavailable, OSD
heartbeats fail and peers report them to the mons as down. The mons send out a map
accordingly, and the affected OSDs report “I’m not dead yet!”. Flap flap flap.
YMMV