Witnessing standby failure with repmgr
Since we're using streaming replication, writes to the master will no longer go through when the standby fails. 


Not necessarily the case.  This is only the case when you are setting up synchronous streaming replication.  Normally the master will return immediately after it writes its own log files to disk and not wait for the slave.  It is then replicated out when the slave requests.

See the synchronous_commit parameter.

I don't see why you need to futz with repmgr for this.