Backups are supposed to be routine maintenance.
You have to be prepared in case something goes wrong.
As certain as you and me will die sooner or later, hard drives will fail.
I have tested the scenario and updated the previous post.
Forced firmware update is not necessary, just format the new drive.
I think something has changed with the new firmware versions.
The data in the drive that stays installed is not touched.
The data in the removed drive also stays unharmed.
So in theory, there is no need to restore.
Another way to read the data, would be to install the 1 TB drive in another LS-WXL unit as the only drive.
But, be aware, if you do so, you will have two units with the same name and maybe IP address on the network.