I've got a persistent volume currently bound to a deployment, I've set the replica count to 0 which I was hoping would unbound the volume - so I could mount it on another pod but it remains in a Bound status.

"Bound" does not mean it is attached to a Node, nor to a Pod (which is pragmatically the same thing); Bound means that the cloud provider has created a Persistent Volume (out of thin air) in order to fulfill a Persistent Volume Claim for some/all of its allocatable storage. "Bound" relates to its cloud status, not its Pod status. That term exists because kubernetes supports reclaiming volumes, to avoid creating a new cloud storage object if there are existing ones that no one is claiming and fulfill the resource request boundaries.

There's nothing, at least in your question, that prevents you from launching another Pod (in the same Namespace as the Deployment) with a volumes: that points to the persistentVolumeClaim and it will launch that Pod with the volume just as it did in your Deployment. You can then do whatever you'd like in that Pod to egress the data.