manual intervention is not required. Patroni will just use a Standby as the new master. If the old master will be alive again it will be started as a backup. Of course there might be dataloss if it was used with async replication.

Patroni has great docs for this here: https://patroni.readthedocs.io/en/latest/replication_modes.h... (Actually this is more or less a thing to do with Postgres)