Yellow Box Factory Reset

If & when I need to do a factory reset of my Yellow Box and do a restore of a backup (saved in Google Drive) will then my Zwave and Zigbee devices come back ?

That depends on which backup has the working Zwave & Zigbee devices. So do you have any ideal on which backup has it working?

I don’t understand your question. I am referring to the HA backup:

Do you know when the issues with Zwave & Zigbee started? What day? What version did it start with? If you go into HA with Samaba, you can check out the backups because it gives some detail on version being backed up.
Without knowing some details like that you’ll be doing a lot of trial/error work.

Restoring the backup should restore your configuration including all integrations and devices.

I recommend testing your recovery process to make sure it works before you need it - the worst time to find out that your recovery process does not work is when you need it.

Disaster Recovery Planning.