At least for the MorefID part of this discussion, actually ESXi IDs are maintained even when the host is connected to vCenter. Simply, vCenter IDs are used. But if both vCenter MorefID and ESXi IDs are stored somehow, I think it would be possible to "failover" to ESXi IDs if vCenter is not available.
However, I see vMotion as a possible issue as ESXi ID will be changed at any host change. This could not easily solved as, if vCenter is down, we don not have any way to track back where the VM has moved based on the vCenter ID (vCenter is down) neither the ESXi ID (changed since last time we checked maybe). Also HA could kick in, without vCenter being u and running.
I see this as a complicated solution, subject to errors in its behaviour, and with limited use cases.
EMEA Cloud Architect @ Veeam Software
Veeam VMCE #1