You can not sync two standalone AO setup. Repository is just contain modules & adapter not activated adapters & module configurations.
We have deal with this situation by putting HA-CDP into DR site with AtriumSSO/AM instance there.
Repository does not have failover feature OOB, but you can come up with cold standby setup which will have latest repository content. (This can be started when primary setup goes down and need to start cold standby repository).
BTW repository does not take part in execution of flows so no immediate impact even though repository is down on execution of flows.