s-j-upload currently allows the uploading of journal logs to a remote server. If this remote server is offline, there is no ability to switch over to a failover system.
I'm not sure if s-j-upload will sit and wait until the target server comes back online, then catch up from where the last cursor entry was. This would certainly provide some backup from infrastructure downtime.
There is a benefit to high security systems, however, in ensuring log files find a way back to central log servers despite system outages. Customer may use central log server for real-time alerting based on certain event types being triggered (i.e. failed logins). Malicious code could try and DOS a log receiver whilst trying to gain entry to the systems that are sending their logs to that server. Having a failover capability in place would increase the ability of logs to arrive at a central system during planned or unplanned outages.