Скорее мой иглиш из бэд и огорчэний оказался, но все равно спасибо.
Делал вот по этой инструкции:
https://www.tecmint.com/setup-redis-cluster-in-centos-8/ Там нет сентинеля, но поведение именно то, что я ожидал, описано.
В офф. доке нашел такое:
"However when the cluster is created (or at a later time) we add a slave node to every master, so that the final cluster is composed of A, B, C that are master nodes, and A1, B1, C1 that are slave nodes. This way, the system is able to continue if node B fails.
Node B1 replicates B, and B fails, the cluster will promote node B1 as the new master and will continue to operate correctly.
However, note that if nodes B and B1 fail at the same time, Redis Cluster is not able to continue to operate."
https://redis.io/topics/cluster-tutorial