I am interested in playing offline D2R on my Xbox One X but have a quick question.
When I upgrade to a Xbox Series X will I be able to transfer my offline characters/progress via cloud/usb storage? (I read this isn’t possible from PS4 to PS5 but I am unsure)
Thanks for reading
Yes your Xbox One makes back ups of all saves to the cloud. As long as you were playing online on the One to sync it, and then have your Series X online when you start the game your save will be there. After the first time you sync it you can then play it offline as well. Your save is stored locally as well as backed up in the cloud.
Awesome, thank you for clearing that up for me 
The Xbox does this for all games as well, not just Diablo. So if you upgrade consoles all your saves will be there as long as you were online on the previous console for the cloud sync to happen.
About terror zone in offline Xbox? This next patch 2.6?