@primofamilia In general when storage node #3 comes back online all changed images will be resynced to the #3 site from the master node. This will happen all automatically. You will have to do nothing more than bring storage node #3 back online.
With that said if your new site #3 will have a different IP address range, or more specifically the storage node will have a different IP address than at the legacy site you will have a little fixing up to do to bring the node back online. But its not that hard to do.