I decided to push my luck and see for real how stable the Windows 10 upgrade scenario is.
The installation I started was centrally deployed via ConfigMgr, and to make it a bit more difficult I decided to start the upgrade over a remote connection and 4G connection. Everything started just fine and the download took some time but it finalized successfully, and the computer restarted and started the upgrade. After an hour or two I had to leave and go to the train, so I dropped the remote connection and the network, pulled the power cord, shut the lid and I was convinced that this would break the upgrade process. Finally on the train I opened the lid on my battery powered computer and the upgrade was just sleeping and continued. Suddenly the logon screen showed up and I logged on with cached credentials, since I had no network connection, user profile got upgraded and the upgrade was done! Desktop still there, documents still there, work folders still there, OneDrive needed reconfiguration, settings still there, computer is still in the domain, pinned apps on the taskbar is still there, remote connection works etc. It just worked! I got really impressed of the work of the upgrade scenario and this is definitely something I recommend you all to try out.