Comment 2 for bug 1774363

What it sounds like you're asking for is the ability to rebuild a shelved offloaded instance in error state, which would actually trigger something like an evacuate operation to build the instance on a new host (like unshelve). That's not supported today, and to add that support would be an API change to rebuild and require a spec:

https://docs.openstack.org/nova/latest/contributor/blueprints.html